stu, how acurate does the tps sensor need to be set?

when i changed mine a couple weeks ago i couldnt get the sucker to give the right readings if i had .5v at idle like it was ment to be then at full throttle it would ony give around 5.2-5.3v
so i set it to around .7v at idle and then i get 5.5v at full chat. seems to run fine but just wondering i spose