Here is one for you. Another tech calls me at home the other night and tells me my manometer is screwed up. He was out on a call that I had done the set up on. Low fire 1.9wc high fire 3.5wc. He tells me my manometer is not working right because he hooked up his and the high fire was 2.8wc so he brought it up to 3.5wc and told the customer that everything was fine now that the gas pressure was set right.
I grab my Dwyer u tube off the truck and hook it up to my furnace and check where it is sitting. 1"3/4 down and 1"3/4 up good 3.5wc. Hook my Testo 506 up and 3.53wc. Guess who has the screwed up manometer and has to go back to the over fired furnace. He is using a UEI manometer I told him at the shop the next morning he better get a new manometer. He then tells me there must be alot of furnaces out there that he has overfired.