On an Index card I make a Roman numeral mark for every album side. 20 minutes per sid. Total divided by 3 is the hours. Not exact. But its closer than the hrs shown on my lawn tractor. I forgot to turn off ignition and it now shows 60-70 more hrs than actual. Same would happen with this timer. Forget to stop and I bet your time is messed up (fubar)
An example iiii/ iiii/ iiii/ =15 sides or 5 hrs
An example iiii/ iiii/ iiii/ =15 sides or 5 hrs