In general, the numbers on a human meter are going to be 20-30 points lower than on a vet meter.
The only place the difference is crucial is when you are seeing numbers in the lower ranges.
For instance, on a vet meter, "normal" BG for a cat is between 70-150. On a human meter, the range is about 40 or 50-120.
Edit - whichever meter you use, just make sure that people are aware of what you are using to test. An easy way to do that is to add it to your signature.
At higher BG ranges, the variance might be greater. But at higher ranges, the difference is not going to have as much importance in terms of "what to do"