All McLeod gauges heretofore constructed with large volumes and fine capillaries have failed to attain the sensitivity, precision, and accuracy which should be expected from the compression ratios. This is due to certain experimental difficulties which are enumerated. Description is given of a large McLeod gauge whose methods of construction eliminate all these difficulties and whose high sensitivity, precision, and accuracy are fully comparable to the gauge's compression ratio of 2.4×10−7. The methods of construction can be applied advantageously to small as well as to large McLeod gauges. At pressures of 10−2, 10−3, 10−4, and 10−5mm of mercury, the precision of this gauge is 0.2, 0.6, 2, and 6 percent, respectively.