The ``metabolism test'' is given before each session on the E-Meter and comes after the can squeeze that sets sensitivity for 1/3 of a dial drop on the PC. The test involves having the PC take a deep breath, holding it for a second, and then letting it out. This is meant to produce a sudden drop or fall (movement to the right) of the needle on the dial, similar to an LFBD. If the needle doesn't move far enough, it is assumed that the PC in not sessionable by reason of being tired or hungry; this simple test is meant to measure what Hubbard calls "basal matabololism", but it unknown to me how it works.
Apparently, there is some connection to taking a deep breath and the restistance of the body dropping, but it is unlikely in my opinion that this has anything to do with how much the PC has slept or eaten. In all likelihood, this is a learned biofeedback mechanism, and can sometimes be used to get out of a session that the PC does not want to take. If the test does not work the first time, often the PC is asked to wait a minute and try again, this time breathing deeper. If this doesn't work, the PC is sent running off to get a candy bar from a machine or some such, eat that, come back, and the test is tried once more. Of course, under normal conditions in Scientology, and especially for staff, the PC is always tired. However, if the PC is deemed "unsessionable" because of poor results on the metab test, he or she is often sent packing to Ethics.