FOR PUBLICATION
  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT

UNITED STATES OF AMERICA,                
                Plaintiff-Appellee,
               v.                              No. 06-50387
MARVIN MCCALEB, aka Marvin                       D.C. No.
Darryl McCaleb; Marvin Darell               CR-03-00849-CBM-
McCaleb; Marvin Darrell                              1
McCaleb; Dary McCaleb; Marvin
                                                 OPINION
McCaleb; Marvin Darryl McCabb;
Morgan; Sammy Jackson,
             Defendant-Appellant.
                                         
        Appeal from the United States District Court
            for the Central District of California
       Consuelo B. Marshall, District Judge, Presiding

                  Argued and Submitted
          November 18, 2008—Pasadena, California

                     Filed January 13, 2009

      Before: Myron H. Bright,* Stephen S. Trott, and
          Michael Daly Hawkins, Circuit Judges.

                    Opinion by Judge Bright




   *The Honorable Myron H. Bright, Senior United States Circuit Judge
for the Eighth Circuit, sitting by designation.

                                493
496                UNITED STATES v. MCCALEB
                          COUNSEL

Verna Jean Wefald, Pasadena, California, for the appellant.

Thomas P. O’Brien, United States Attorney, Christine C.
Ewell, Assistant United States Attorney, and Janet C. Hudson,
Assistant United States Attorney, Los Angeles, California, for
the appellee.


                           OPINION

Bright, Circuit Judge:

   Appellant Marvin McCaleb challenges his drug-related
convictions and sentence to life imprisonment, asserting that
the district court (1) improperly instructed the jury, (2) abused
its discretion by admitting certain expert-witness testimony,
and (3) relied on unproven prior convictions. Because the dis-
trict court did not (1) plainly err in its jury instructions, (2)
abuse its discretion by admitting certain expert-witness testi-
mony, or (3) improperly rely on unproven prior convictions
at sentencing, we affirm.

          FACTS AND PROCEDURAL HISTORY

   In November 2004, a federal grand jury returned an indict-
ment against McCaleb and other individuals. Count One of
the indictment charged McCaleb and other defendants with
conspiracy to manufacture, to aid and abet the manufacture
of, to distribute, and to possess with intent to distribute, phen-
cyclidine (“PCP”), in violation of 21 U.S.C. §§ 846 and
841(a)(1), (b)(1)(A). Count Two of the indictment charged
McCaleb and two other defendants with possession of ethyl
ether, a precursor chemical, knowing and having reasonable
cause to believe that it would be used to manufacture PCP, in
violation of 21 U.S.C. § 841(c)(2).
                   UNITED STATES v. MCCALEB                   497
   McCaleb and a codefendant’s trial began in March 2005.
At trial, McCaleb conceded guilt on the lesser-included
offense in Count One, conspiracy to possess ethyl ether, and
Count Two. In April 2005, the jury returned guilty verdicts on
Counts One and Two. Ambiguously, the jury also found
McCaleb guilty of Count One’s lesser-included offense. After
the clerk read the verdict in open court, the district court cal-
led counsel to sidebar and stated the following:

    According to our instructions, the jury should have
    only answered [the lesser-included offense] if they
    found the defendant not guilty of Count 1. So what
    I would be inclined to do is just to indicate to them
    that they should go back and give them another ver-
    dict form, and they should be clear as to whether
    they find the defendant guilty or not guilty as to
    Count 1. And if they find the defendant not guilty as
    to Count 1, then they shouldn’t answer [the question
    about the lesser-included offense].

    ....

       So I would . . . give them another verdict form and
    ask them to be clear about that and then to return
    that.

   Without objection from either party, the district court told
the jury the following: “Ladies and gentlemen of the jury, in
looking at the verdict forms that you have returned for each
of the defendants, it is unclear as to what you intended your
verdict to be as to Count 1 of the indictment.” The district
court then stated:

       So, if you intended as to Count 1 to find the defen-
    dants not guilty, then of course you would consider
    the necessary lesser included, and you would advise
    the Court as to your verdict.
498                UNITED STATES v. MCCALEB
         You would then date, sign the verdict form, and
      return it.

         If — on the other hand, if you find the defendants
      guilty as to Count 1, then you don’t indicate any-
      thing in the blank for the necessary lesser included.
      I think that’s consistent with the instruction. But
      maybe we just didn’t explain it very well.

After this instruction, the district court gave the jury a clean
copy of the verdict form and told the jury to “retire, continue
deliberating.” And after further deliberations, the jury
returned a verdict finding McCaleb guilty on Counts One and
Two. In accordance with the alternative nature of Count One
and its lesser-included offense, the jury did not fill in the
lesser-included-offense blank on the verdict form.

   After the guilty verdicts, the trial resumed on the issue of
drug quantity, and, in May 2005, the jury returned a special
verdict finding that the amount of PCP involved in Count One
was at least 100 grams. The jury’s quantity finding and evi-
dence of McCaleb’s two prior felony drug convictions trig-
gered a statutorily mandated life sentence for Count One. See
21 U.S.C. § 841(b)(1)(A). In June 2006, the district court sen-
tenced McCaleb to life imprisonment on Count One and a
concurrent 240-month term on Count Two. This appeal fol-
lows.

                         DISCUSSION

                               I.

   McCaleb did not object to any of the jury instructions that
he now challenges on appeal. Accordingly, we review
McCaleb’s jury-instruction claims for plain error. See United
States v. Marchini, 

, 767 (9th Cir. 1986); see
also Fed. R. Crim. P. 52(b). Under this standard, a defendant
must show an “error” that is “plain” and that “affects substan-
                   UNITED STATES v. MCCALEB                   499
tial rights.” See United States v. Olano, 

, 732
(1993). Even when a defendant makes all three showings, we
will exercise the discretion to reverse a conviction only if the
error seriously affects the fairness, integrity, or public reputa-
tion of judicial proceedings. See 

contends first that his convictions should be
reversed because the district court “sua sponte vacated the
verdict . . . on the grounds that it was inconsistent as to count
one, and then ordered the jurors to resume deliberations,
resulting in an unauthorized second verdict that was necessar-
ily coerced.”

   [1] “Any criminal defendant . . . being tried by a jury is
entitled to the uncoerced verdict of that body.” Lowenfield v.
Phelps, 

, 241 (1988). Coercion can occur when,
for example, a district court tells a jury that it must reach a
decision, Jenkins v. United States, 

, 446 (1965),
a district court polls a jury before it reaches a verdict, Bras-
field v. United States, 

, 449-50 (1926), or a spe-
cial verdict form “reformulate[s] the elements of the crime,”
United States v. Reed, 

, 1181 (9th Cir. 1998).

   [2] We conclude that McCaleb’s assertion that the district
court coerced a verdict lacks merit. The record shows that the
jury found McCaleb guilty both of Count One and Count
One’s lesser-included offense. In such circumstances, a dis-
trict court may treat the guilty verdict on the lesser-included
offense as surplusage. See, e.g., United States v. Howard, 

, 563 (8th Cir. 1974). If a district court can disregard
a guilty verdict on a lesser-included offense, then it does not
plainly err by asking the jury to clarify its verdict. After dis-
covering the ambiguity, the district court here instructed the
jury on the alternative nature of these offenses and asked the
jury to clarify its verdict. The district court stated that it
ordered the jury to reconvene because it was “unclear as to
500                   UNITED STATES v. MCCALEB
what [the jury] intended [its] verdict to be as to Count 1 of the
indictment.” Moreover, as McCaleb concedes, “the [district]
court may ask the jury to clarify an inconsistent or ambiguous
verdict.” See Larson v. Neimi, 

, 1402 (9th Cir.
1993) (stating that such a practice “comports with common
sense as well as efficiency and fairness”).

   [3] The cases McCaleb cites in support of his argument are
distinguishable. In Jenkins, the Supreme Court reversed a
conviction because a district court had instructed a dead-
locked jury that it must reach a verdict. 

.
But the jury here was neither deadlocked nor told that it must
reach a verdict. Similarly, this Court held in United States v.
Pino-Noriega that a defendant waives his right to testify in his
defense by waiting until after the jury had reached its verdict
to inform the district court that he wanted to testify. See 

, 1094-96 (9th Cir. 1999). But nothing in Pino-
Noriega limits a district court’s authority to clarify an ambig-
uous verdict. Thus, we conclude that the district court did not
err.1

                                     B.

   [4] McCaleb also challenges his conviction on Count One
by arguing that the district court “failed to instruct on the ele-
ments of the four objects of the conspiracy, thereby lessening
the prosecution’s burden of proof.” It is well-established that
a district court errs if it fails to instruct the jury on an element
of a charged offense. See United States v. Alghazouli, 

, 1189 (9th Cir. 2008), cert. denied, 

(2008). Similarly, a district court plainly errs in a conspiracy
case if it “fails to instruct the jury on an element of the crime
that is the object of the conspiracy.” 

makes much of the district court’s decision to “vacate” the
verdict, arguing that a district court has no authority to vacate a verdict
because it is inconsistent. But the district court did not vacate the verdict;
it simply asked the jury to clarify an otherwise ambiguous verdict form.
                     UNITED STATES v. MCCALEB                       501
   To prove a conspiracy, the government must show “(1) an
agreement to engage in criminal activity, (2) one or more
overt acts taken to implement the agreement, and (3) the req-
uisite intent to commit the substantive crime.” United States
v. Sullivan, 

, 976 (9th Cir. 2008) (quotation
marks omitted).

   McCaleb argues that the district court did not instruct the
jury on the elements of manufacturing PCP, one of the four
objects of the conspiracy. The elements of manufacturing
PCP are straightforward. The government must prove that a
defendant “(1) knowingly or intentionally (2) manufactured
[PCP].” United States v. Basinger, 

, 1406 (9th
Cir. 1995).

   [5] Here, the district court’s jury instructions as a whole
sufficiently apprised the jury that the objects of the offense
had a mens rea component. McCaleb’s argument, therefore,
turns on whether the district court plainly erred by using, but
not defining, the term “manufacture.” A district court does not
commit plain error by failing to define a word when it “is a
common word which an average juror can understand and
which the average juror could have applied to the facts of
[the] case without difficulty.” United States v. Chambers, 

, 1460 (9th Cir. 1990) (holding that failure to define
“knowingly” was not plain error); see also United States v.
Garza-Juarez, 

, 910 (9th Cir. 1993) (holding that
failure to define “possession” was not plain error). We con-
clude that the district court did not commit plain error by fail-
ing to define manufacture, particularly when it instructed the
jury that any undefined word in the instructions “means just
what you think it would mean, the ordinary meaning.”2
  2
    The government must prove only one of the objects to support a con-
spiracy conviction. See 

. Here, the jury “unani-
mously agree[d]” that McCaleb had conspired to commit each of the four
objects. Thus, because the jury’s instructions on manufacturing PCP were
sufficient to convey the elements of that offense, we need not consider
McCaleb’s challenges to the district court’s instructions for the other
objects.
502                UNITED STATES v. MCCALEB
                               C.

   McCaleb contends next that the district court gave a plainly
erroneous jury instruction at sentencing. After the jury found
McCaleb and his codefendant guilty, the district court
instructed the jury as follows:

      [N]ow that you have reached a verdict and having
      returned a verdict of guilty as to each of the defen-
      dants, you will now be asked to complete a special
      verdict form specifying whether the amount of PCP
      involved in each defendant’s commission of the
      offense charged in Count 1 of the first superseding
      indictment exceeded a specified quantity.

(Emphasis added.)

   McCaleb argues that this instruction constituted plain error
because “each person involved in a conspiracy may be sen-
tenced only for the quantity of drugs that he reasonably fore-
saw would be distributed or manufactured, or that fell within
the scope of his agreement with his coconspirators.”

   In United States v. Becerra, this Court stated that “[u]nder
the [Sentencing] Guidelines, each conspirator may be sen-
tenced only for the quantity of drugs that he reasonably fore-
saw would be distributed or that fell within the scope of his
own agreement with his co-conspirators.” 

, 966
(9th Cir. 1993). But in United States v. Mesa-Farias, this
Court clarified that “[t]he reasonably foreseeable test of
Becerra limits a conspirator’s liability only for drugs pos-
sessed by a coconspirator, not for drugs possessed by the con-
spirator himself.” 

, 260 (9th Cir. 1995).

   [6] Thus, the district court was not required to give the
“reasonably foreseeable” instruction in this case. As the dis-
trict court aptly concluded in its order denying McCaleb’s
motion for a new trial:
                   UNITED STATES v. MCCALEB                   503
    [T]he Government offered evidence that both
    McCaleb [and his codefendant] possessed and partic-
    ipated in the delivery of amounts of precursor chemi-
    cals that were more than sufficient to produce 100
    grams of PCP. Therefore the issue of foreseeability
    as set forth in [Becerra] is not an issue because there
    is no foreseeability requirement for the quantities
    possessed by [McCaleb].

(Emphasis added.) And the fact that McCaleb possessed pre-
cursor chemicals, and not PCP itself, is of no moment because
the jury found McCaleb guilty of Count Two, possessing
ethyl ether either knowing or having reasonable cause to
believe that it would be used to make PCP. We conclude that
the district court did not plainly err.

                               II.

   McCaleb argues next that the district court improperly
admitted the testimony of a Drug Enforcement Administration
(“DEA”) forensic chemist because that testimony was insuffi-
ciently reliable under Daubert v. Merrell Dow Pharm., Inc.,

(1993). We review a district court’s decision to
admit expert opinion testimony for an abuse of discretion. See
United States v. Gonzales, 

, 909 (9th Cir. 2002).

   Federal Rules of Evidence 702 allows for the admission of
“scientific, technical, or other specialized knowledge” when
“(1) the testimony is based upon sufficient facts or data, (2)
the testimony is the product of reliable principles and meth-
ods, and (3) the witness has applied the principles and meth-
ods reliably to the facts of the case.” A district court may rely
on various factors in evaluating such evidence, including (1)
whether the theory can be or has been tested; (2) whether the
theory has been subjected to peer review; (3) whether the
error rate is known and standards exist to control the opera-
tion of the technique; and (4) whether the theory has gained
general acceptance. 

. A district
504               UNITED STATES v. MCCALEB
court is not required to “mechanically apply the Daubert fac-
tors” and has “broad discretion when discharging [its]
gatekeeping function.” United States v. Hankey, 

, 1168 (9th Cir. 2000).

   [7] The specific claim of error relates to permitting a DEA
forensic chemist, A. Harman, to testify about the actual yield
of PCP that could be produced in a clandestine laboratory for
purposes of establishing the fact that the conspiracy in Count
One involved more than 100 grams of PCP. We see no error.

   First, Harman testified that the 25% figure was “based on
an aggregate of data compiled by the DEA” from seizures
from clandestine laboratories. Harman testified that the DEA
maintains an internal database, which contains data on the
actual yield of PCP produced in clandestine laboratories and
that she reviewed an e-mail from “headquarters,” which indi-
cated that the average yield from such laboratories was
between 30% and 40%. Thus, Harman opined that the 25%
figure was a “conservative estimate” of actual yield in a clan-
destine laboratory. Harman’s testimony was not, therefore,
based on “unsubstantiated speculation and subjective beliefs.”
See Diviero v. Uniroyal Goodrich Tire Co., 

, 853
(9th Cir. 1997). Moreover, Harman stated that the 25% figure
is “commonly used,” by “forensic chemists throughout DEA.”
Harman testified that there are “an average of 30 chemists in
each of the [DEA’s] eight laboratories.” See 

(noting that general acceptance among scientists
bears on reliability).

   Second, Harman testified that she was familiar with a study
published in the Journal of Medicinal Chemistry regarding
actual yields of PCP in a laboratory. And the district court
noted that Harman’s opinion, at least in part, is “based on
published articles.” See 

(stating
that publication is one means to establish the reliability of a
scientific theory or methodology).
                  UNITED STATES v. MCCALEB                 505
   Finally, Harman stated that when she synthesized PCP in
her laboratory, she obtained an actual yield of about 55%. She
testified that she considered this yield when she opined that
a 25% yield in a clandestine laboratory is a conservative esti-
mate. And Harman testified that one of the purposes of her
efforts to synthesize PCP was to “mak[e] a determination on
the issue of actual yield.” We conclude that the district court
did not abuse its discretion by admitting Harman’s testimony.

                             III.

   [8] Finally, McCaleb challenges his sentence, arguing that
“because [his] prior convictions were not found true by a jury
beyond a reasonable doubt, they cannot be used to enhance
his sentence to life imprisonment.” Reviewing the constitu-
tionality of his sentence de novo, United States v. Flores-
Sanchez, 

, 1093 (9th Cir. 2007), cert. denied,

(2007), we conclude that the district court did
not improperly rely on McCaleb’s prior convictions. See, e.g.,
Almendarez-Torres v. United States, 

, 226-27
(1998) (holding that a prior conviction that increases the
defendant’s sentence may be decided by the judge, not the
jury); 

(same).

                       CONCLUSION

  Accordingly, we AFFIRM McCaleb’s convictions and
sentence.