EX-24

POWER OF ATTORNEY


KNOW ALL BY THESE PRESENTS, that the undersigned, Justin Spencer, hereby
constitutes and appoints Douglas Carlen, Chi-Mei Cheng, and
Lydia Terrill, the undersigned's true and lawful attorney-in-fact to:

(1)     Execute for and on behalf of the undersigned a Form ID, Uniform
Application for Access Codes to File on EDGAR ("Form ID"), in accordance with
Section 16 of the Securities Act of 1933, as amended (the "Securities Act"),
and the rules thereunder;

(2)  Do and perform any and all acts for and on behalf of the undersigned which
may be necessary or desirable to complete and execute any such Form ID and
timely file such form with the U.S. Securities and Exchange Commission; and

(3)  Take any other action of any type whatsoever in connection with the
foregoing which, in the opinion of such attorney-in-fact, may be of benefit to,
in the best interest of, or legally required by, the undersigned, it being
understood that the document executed by such attorney-in-fact on behalf of the
undersigned pursuant to this Power of Attorney shall be in such form and shall
contain such terms and conditions as such attorney-in-fact may approve in such
attorney-in-fact's discretion.

The undersigned hereby grants to such attorney-in-fact full power and
authority to do and perform any and every act and thing whatsoever requisite, or
proper to be done in the exercise of any of the rights and powers herein
granted, as fully to all intents and purposes as the undersigned might or could
do if personally present, with full power of substitution or revocation, hereby
ratifying and confirming all that such attorney-in-fact, or such attorney-in-
fact's substitute or substitutes, shall lawfully do or cause to be done by
virtue of this Power of Attorney and the rights and powers herein granted
related to the Form ID.  The undersigned acknowledges that the foregoing
attorney-in-fact, in serving in such capacity at the request of the
undersigned, is not assuming any of the undersigned's responsibilities to
comply with Section 16 of the Securities Exchange Act of 1934, as amended.

This Power of Attorney shall remain in full force and effect until the
undersigned is no longer required to file Form 3, 4 or 5 reports with
respect to the undersigned's holdings of and transactions in securities
issued by the Company, unless earlier revoked by the undersigned in a signed
writing delivered to the foregoing attorney-in-fact.

IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to be
executed as of the 4th day of June, 2019.

/s/ Justin Spencer by Douglas Carlen attorney-in-fact
Justin Spencer