Hydrometer, correct use

[trubled]

temp within reason isnt all that important because there is so much flux with the meter.
what is important is insuring CO2 isnt grabbing onto the instrument -- if this sounds wrong take your hydrometer and put it in a test tube full of half fermented beer and watch it rise a number of points.

 

[ajdelange]

CO2 can be adequately dealt with in fermenting beer by the use of a second cylinder somewhat larger than the hydrometer jar. Fill the second cylinder with more than it takes to fill the one that you will use for the measurement. Place your clean, dry hand (or other more suitable closure) over the jar and shake like mad. Open the closure just enough to let the gas escape, let the jar settle for a minute or 2 then repeat. Now pour the liquid into the smaller jar to near the lip. Then lower the hydrometer into the jar so it overflows as I described in an earlier post. If any foam remains, just blow it away. Then read. If you want a second reading some time after the first (after the sample has warmed, for example) bubbles will form on the body of the hydrometer. Just give the stem a spin in this case.

I have found I can read narrow range hydrometers on a gassy sample to an accuracy of 0.1 °P using this technique.