Well, a calibration file something is that will come with a microphone to show it's frequency response.
If you use a mic or meter that we have tested on the site, then you can get away with using those calibration files (if you own one of those), with an assumption that they're accurate enough for home use. We have cal files for all the Radio Shack meters,
Galaxy CM-140 meter and the ECM8000 microphone. The Radio Shack meters shouldn't be used much beyond 1000Hz as it seems as they aren't accurate past that. The ECM and Galaxy are full range. The ECM requires a preamp though.
If you don't have a cal file for the microphone you own, then you have no way of knowing its accuracy I'm afraid.
brucek