English: An old McLeod gauge is low pressure measuring instrument, which is used for high precision measurement of vacuum. As shown, it has been drained of mercury. This gauge is on display in the lobby of the Science building at Winthrop University. The vacuum port is not visible in the photograph; it runs through the center bearing and opens on the far side. The left hand column is sealed off at the top; this is visible by zooming in on the picture. The gauge was rotated clockwise to reset and counterclockwise to measure. Photo by Yannick Trottier, April 10th, 2006.