My mom worked at GTE and when I went to college in 1997 she got us a WATS line so I could dial 1-800 to call home. One of her jobs in the early 80s was to calc

My mom worked at GTE and when I went to college in 1997 she got us a WATS line so I could dial 1-800 to call home. One of her jobs in the early 80s was to calculate the bills for WATS lines. There was a room full of mechanical counters, like odometers, that would increment while people were talking on their line. Every day she'd write down the new counts, subtract the previous day's counts, and they'd bill the difference.