I cannot help you about the counter staff, but I used to work in a bookies many many moons ago. I was in the back office, taking the telephone bets and working out the returns. We had ready reckoners as it was before the days of calculators.
I absolutely loved it.
Didn't start until nearly lunch time, work was either totally hectic or not a lot to do (mostly hectic, people want their returns pretty quickly) and the time just flew in.
I expect it will be similar on the counters.
Occasionally if a regular punter had a big win, we got chocs from them.
This was in a very tiny back street bookies.
Give it a go.