ORIGINAL: gaRCfield
For an accurate reading you also need to discharge it at a specific rate otherwise your numbers will be slightly off. I forget what the rate is, but maybe someone else knows? Is it C/5?
You are correct, C/5 and you need to drop down to 0.9 volts/cell during the discharge if you are comparing capacity to factory specs. If you discharge at a higher rate or only down to 1 or 1.1volts/cell you will get a lower number of MAH's.