Accurate to within plus or minus 3%. The McLeod gauge is the most convenient and economical instrument for measuring low pressures from 1 micron up. The ACE McLeod gauge is offered in four ranges, so that it is possible to accurately measure any pressures between 1 micron and the highest reading on our D size, which is 15mm. All gauges are fabricated from calibrated ACE Trubore tubing, to assure uniform and reproducible readings between gauges. Joint is standard taper 20/65. Mercury NOT supplied.