what causes private market unit availability too lower?

if you login with full pm and don't empty it completely then units in pm will be diminished on next login.

Are you sure marshel?
I think only the replanishing rate of the narket will be diminished and not the units there

yea replenish rate.

these things should be at wiki.

Cosmo
If you search on google
Market replenishment empire earth
You will find a thread with the explantion

ok thanks

well its basically replenish vs diminish rates, if your market is above its standard size for your land then their is no replenish rate to fight the diminish rate so it lowers until the 2 balance out and it stays static assuming you are logged in constantly refreshing the page. If you log in and you above your standard rate even if you log out it will diminish until the 2 balance out but it will go back up again above standard if you stay logged out during the whole thing.