Measures in excess of 10 US gallons are commonly referred to as provers. The stainless steel prover is equipped with an overflow trough and drain-cock to prevent voiding your test. Series J Provers are made with a well-pitched bottom with a center draught connected to a drain brought forward to a shut-off value and are equipped with three heavy duty legs. In each unit, the neck is equipped with a center draught connected to a drain-cock for setting the measure at zero when the neck test measure is to be drained into the device being tested. The inside is constructed so that the prover is free of bubbles when filled to assure that no liquid is entrapped when the unit is drained. Gauge fixtures are entirely on the outside of the neck of the unit to keep the neck free from any construction or obstruction, and to assure the accuracy of the area of the neck at each graduation throughout the length of the reading scale. All parts of the gauge fixture can be removed and reassembled at will without the slightest danger of damage or change of accuracy as long as the lock pin is not removed. Also, adjustments can be made without emptying the measure or taking it apart, by first removing the seal and lock pin and then turning the adjusting rods to the change desired. Measures are equipped with two leveling gauges and a standard “butterfly” valve. Provers the same basic features as used in the models, however they are normally mounted onto a transfer tank. The 5-Gallon and 20-Liter Special vessels fit onto a stainless steel ball joint to support the measure eliminating the need for legs, but still having a bottom drain. Special provers up to 150 gallons (500 liters) can be fitted with crank legs that are adjustable as well as capable of bolting down.