Bosch DLR130K. You can get it on Amazon around $80. Might sound a little pricey but it turned out to be the most important tool I've ever used in my listening room. Once you own it you will wonder how you ever managed properly without it. Precise measurements to 1/16th inch. It's NOT overkill...every speaker set up will be dramatically easier and sound dramatically better than if you didn't use it. Don't hesitate. It is exactly what you are looking for. You will thank me, I guarantee it.
Happy Lissn'n
Happy Lissn'n