I have a autometer Phantom boost gauge and Greddy Profec B Spec 2. The two have different readings. At idle, the autometer reads -13ish while Greedy reads -6ish. When the engine is off, the autometer is at 0 while greddy is -2. How can I get these two to sync? which one should I trust?

 

If the engine is off then it should read 0. Neither is going to be super accurate unless they support a way of calibrating them for your particular elevation. So just use them to give you a rough idea of what your boost is but very likely they are +/-1->3psi off

 

Your Greddy gauge is about as worthless as a flat tire!

 

Update: When in vacuum, the autometer phantom gauge reads in hg while greddy reads in psi. When i use a converter, its very close...off by 1 or so. Basically, it was two different measurement units!