A high-tech method......
I mix and track with 2 led's (out of 5) lit on the front panel of my monitor amp. I decided on that as a standard because my reference material sounds best ( in that room with those speakers) at that level. I ( my ears) can hold out much longer and my brain's ability to process the sounds and percieve depth and dimension seems to hang in longer at a moderate level. It took me a long time to figure it out, but standing in front of a full stack for hours at a time has a cost. Though it's been a couple of years since I did that, I still occasionally get a ringing at about 6KHz, and running my studio mon's at high levels aggrevates it.
Not very precise I'm afraid but works for me>>>
chazba