Lower abundance counts yet sensitivity the same

[MSCHemist]

I am running a method on the GC/MS and comparing it back 4 months. At the lowest calibration I see that my peak heights are 5-10 fold lower but the signal to noise for the peak and everything is the same. It looks like the whole chromatogram was shrunken down by 5-10 fold including the noise level in terms of abundance counts. I compared the tunes from now and back then and there is no significant differnce.

Any idea what could cause it?

[Pepter]

Your EMV on the same lvl ?

[MSCHemist]

Yep the emvolts have been in the 1800's and 1900's for several months. The method uses the atune.