Personally, we like to do it with the grip off. That being said, it is completely OK to do it with the grip on. With grips, numbers can vary, depending on the size and firmness of the grips. We just feel it’s a truer representation without a grip. It’s all relative, in that you are really just comparing numbers or looking at a progression. As long as you are comparing grip on to grip on or grip off to grip off, the data is useful. You will not get the same numbers, obviously, comparing a grip on to a grip off of the same club, but in a set the progression or slope should be the same (just at a different point on the chart). Depending on what kind of chart you are using, some are based on grips on and others are based on grips off. The one we sell is based on grips on. We have listed on our website charts that based on grips off. I have put the links below. You should be able to print them out and use them. The one we sell in a pad is code number GLFMC and is grips on.
One link shows a chart for woods and irons and the other is a chart for irons that we overlay with several different sets that we tested and where they fall. The color ranges show the variance you can get, depending on the manufacturer and shaft model. The ranges are based on literally thousands of shafts we have in our database.