ORTF - Drum Overhead Centering Trick

I've been using the ORTF micing technique for drum overheads for many years.  I recently shared a trick I use to make sure your snare and kick drums end up in the center of the stereo image (if that's what you're wanting).  Take your phone, transistor radio, or any small device that can play audio at a decent level through it's speaker and place it on the center of your snare drum.  While playing some audio (mono) through the device, go into the control room and adjust the gain of your overhead mics to the same level on each of the left/right channels (also flip one mic out of phase and check for mono cancellation).  This time, by placing the device on the top of the kick drum on the beater end, do the same for the kick drum to see/hear if it is centered.  If not, you can move your ORTF pair around a bit until you get snare and kick centered.  After going through this process a couple of times, you'll get the hang of it.  It's fast and great for getting the snare and kick centered before the drummer gets there for the session and for getting the overall overhead microphone levels right.  You will also get the hang of how much acoustic level out of the playing device will get you the correct record level at the board.