Compensating timer circuit diagram

There was (at one time, in the not-too-distant-past) a circuit diagram for a (simple) compensating timer posted on the web. It read the intensity of the enlarger's light and modified it's timing accordingly (like the various commercial compensating timers.)

It may have been a metronome (beeping) sort IIRC.

I've lost the URL...Does anybody out there in APUG land happen to know of it?

Thanks, Dave