The things that effect compression checks are, your gauge may not be calibrated the same as the guys gauge to which you are comparing your numbers, and the barometric pressure on a given day affects the reading. This means that you could have different readings on different days with the same gauge if a high or low pressure weather front should role through on day two. Don't get hung up on the value of the actual number as long as the difference between cylinders is not significant. Could all cylinders/valves be worn exactly equal and give low readings within 2% of each other? Possible I suppose, but extremely unlikely.
