Problem mrc SNF 2006-08-03 13:46:05: zero drifting for mtorr pressure

[calarrudo at snf.stanford.edu]

Gate valve completely open reads less than zero in pressure mtorr.  If I set my pressure to 10 mtorr based on the less than  zero my wafers are over etching. If I set my pressure higher to 
12.0 mtorr my wafers now etch correctly.  Please check the 
manometer zero to see if it has drifted and make corrections 
please.