In an earlier post I said I used a small engine valve spring compressor and it worked fine for years. I also used an inside caliper. On the older Snapper RER's, uneven cut was a common complaint on mowers brought into the shop. Especially if the customer used a grass catcher. A Snapper factory guy told us that the blade should cut approx 1/4" to 3/8" lower in the front than in the rear so that the blade didn't have to double cut. And always level from side to side.