Sadly the gauge at same place also does not read the same everytime. I used to constantly fill air only at one pump. One fine day suddenly my linea started jumping a giving earthquakes while travelling on rough road. I pulled over a tyre shop and checked the air pressure. Holy cow all tyres were filled with 48psi. Next time i visited the same pump and told him this problem. then he said that every 15-20 days they calibrate the gauge. Last time there was big problem, but now its corrected. Now i have my own Digital air gauge bought off ebay for 599 rs and it works perfectly. All my investigations have revealed that many times the same pump fills different levels of air. Now even when they fill more i can easily correct it with my new gauge.