The CAHN microbalance is found in the balance room.  The instrument is sensitive to even small air movements, so be sure the door to the room is closed as well as the door to the weighing chamber.  The calibration mass is found in the chamber to the right.  The use of this balance is where most of the error for the whole experiment is found.  The digital readout must be stable before it should be recorded.  If the weighing platform is precessing or swinging, it will give an inaccurate mass, stop these motions or wait for them to stop before massing the sample.  Be very patient with this part of the analysis, it is integral to getting quality results from the CHN.