I only take one gravity reading on brew day when brewing with extract -- once the wort is cooled and in the fermenter and right before I pitch the yeast. When brewing with extract there is no need to take any other reading.
For my PM brews I take a reading after mashing and before adding extract to determine efficiency, then again after adding extract so I can hit my preboil targets. Then I take my same OG reading from the fermenter.
jadeddog,
what about the PM reading before the extract. Most of mine are steeped grain. If I take a reading, just put it in the freezer or what to cool down before reading or do you convert based on temp? then can't you add or subract extract to make your OG?
just enter the SG and volume at the time of the first sample, enter your volume, target gravity and gravity of extract for final and it will give you exactly how much extract to add. it works rather well if i do say so myself
you don't need to measure for steeped grains either. steeping and mashing are not the same thing. Steeping is for color, mashing is for actual fermentables.