K'zayis as a weight measurement

The label of the one-pound box of Cohen Halperin Shmura Matza reads:

משקל כל מצה כשיעור כזית

In English (with some Hebrew thrown in, in transliteration, of necessity), that's:

The weight of each matza is the measure of a k'zayis.

Isn't k'zayis a volume measure?

Answer

There is a famous machlokes whether kzayis is a volume or weight measure. Many sefardim follow the Kaf Ha'Chaim that it is a measure of weight.

http://www.vbm-torah.org/pesach/pes62-yr.htm

...As the Maggid Mishneh explains, the Rambam here establishes that these measurements are determined by volume, not weight, a principle that seems to emerge as well from the mishnayot (Keilim 17:6 and elsewhere) and many other sources. This is also the view of the Mishna Berura (486:3). However, the Kaf Ha-chayim (168:46) observes that common practice was to calculate according to weight, seemingly against the straightforward reading of all the poskim. We may perhaps attribute this practice to the difficulty involved in constantly measuring volume.

Today, Ashkenazim calculate volume, in accordance with the aforementioned ruling of the Mishna Berura, and this is also the oft-cited view of Rav Yosef Shalom Elyashiv. The Sefardic authorities dispute the issue: Rav Ovadya Yosef (Yechaveh Da'at 1:16) writes that the weight measurement should be used, while Rav Shalom Messas (Tevu'ot Shemesh) maintains that we determine measurements based on volume.