[Ari Ben Canaan]

When decomposing a carbonate by heating it in a flask and then collecting the maximum carbon dioxide given off.... What is the protocol for taking readings ?

Do you simply wait for the reaction to end and then IMMEDIATELY record the CO2 volume in the syringe ?

Or do you wait for the gas to cool down a bit before taking the reading ?

[Scienceisgood]

I would assume wait for it to call down.

This is because of the basic gas equation PV = nRT.
Increasing temperature increases volume of a gas. So, cooling it down to a suitable temperature (standard temperature) would probably be best to get an accurate reading.