In case anyone is looking for a cheap way to double check your Makita RPM speed, I just tried out a Neiko tachometer I got off Amazon for about $30 bucks. Speeds match up to the Makita speed chart floating around here (search forum).
Can’t vouch for how accurate or how long it will last but for my needs, I’m pretty happy with it. Can also use it on drill press and other rotary tools as well. The reflective tape it uses can be replaced/substituted with reflective foil tape if you run out. Just a helpful FYI…
TIP: This is one of those garage tools you’ll want to take the batteries out of if you don’t use it very often. Otherwise they’ll corrode over time. Throw the ones that came with it in the trash. Use quality grade batteries for less hassle.