plus or minus 2 psi for measuring. alarms at 12.5 and 25% or 2.8psi over a short period of time. the link below is for the newer version than what i have, but i think just the monitor is different. the sensors on the valve stem are easy and do not leak, but do require a battery change by sending them into the factory for a swap. i have had mine for about 2 years so far and they still work good.
http://www.doranmfg.com/PDF/Doran360RVbrochure.pdf
tom