Ph / ppm meter help

I got a meter from my buddy .
http://www.hannainst.com/usa/prods2.cfm?id=028003
He gave me 7.01 and 4.01 solutions . I calibrated it . But when I put the meter back in the solution , it reads 4.05 and 6.98 . So are is the eye messed up and needs replaced ? Or is that within the tolerance of the meter ?I did use tap water between solutions , could the tap water effected the solutions Ph level ? tia

That difference is totally insignificant for what we are doing. And just calibrating it to one or the other is fine, save the solution it works as storage solution too.

So how do you know when the eye needs changed ? Will it not read or not stay on a constant number or what ?