The Exact-air™ pressure meter is used to test the percentage of air in a freshly mixed concrete sample. The test method is based on Boyle’s Law and releases a known volume of air at a known pressure into the concrete sample which contains an unknown volume of air. The resultant change in the sample’s volume correlates directly to the percentage of entrained air in the sample and can be read directly from the gauge. The Exact-air™ pressure meter is made from the highest quality components for years of trouble-free service. Comes with Exact-air™ pressure pump, stainless steel gauge. Meets ASTM C-231, AASHTO T-152, BS-1881.