the thing with on-board gauges is they are not as accurate as a gun, like stated above, there is a wire that wraps around the bottom of the cooling head and takes the temp from there. i use venoms on-board gauges on my whips, but i also have an HPI gun to calibrate the on-board so i kno how much off it is....the only reason i use on board is because I've lost 2 handheld guns, if you are prone to losing your equipment or forgetting where u put it, id invest in a on-board,, but every r/c enthusiast should at least own a gun,, because u can use them for other readings as well..thats my 2 cents