The McLeod gauge can measure vacuums as high as 10 " 6 torr ( 0.1 mPa ), which is the lowest direct measurement of pressure that is possible with current technology.
12.
However, condensible gases, such as water vapour, ammonia, carbon dioxide, and pump-oil vapors may be in gaseous form in the low pressure of the vacuum chamber, but will condense when compressed by the McLeod gauge.
