I've actually yet to pull a harvest off my tables, they are a very recent addition to my garden. 21 per tray is correct.
I'm expecting between a quarter and half ounce per plant this round, i expect to have it dialed in within a couple months and to get closer to an O per. Of course this is all speculation. http://www.rollitup.org/hydroponics-aeroponics/6592-get-harvest-every-2-weeks.html My sog is loosely based on al b fuct's garden, you'd be well served to read everything hes ever written.