Appreciate some advice on using this calibrator. The pointer is not sitting on zero, but slightly below zero. Is there a reason for this? Also, do I adjust the pointer to zero or subtract this offset from my span when calibrating instruments. For example, I want to calibrate a pressure transmitter over the range of 0 to 500 mmWG. If the pointer is sitting at -6 mmWG do I use this as my zero, and 494 mmWG on the Wally Box as my 500 mmWG span? Appreciate any help. TIA