Hi I would like to keep my truck and RV tires properly inflated but I don't know how to do this. I have 4 gauges that I thought were good, ranging in price from $12 to $40. Maybe this is the cheapo range I do not know. All I know is that not one of the gauges read the same. One of them is as much as 15#'s different. Can anyone tell me where to buy a tire gauge that I can rely on?