Techy geek of a certain age required

Another street market archive shot. Between the abacus and the electronic calculator came the comptometer. I had the "experience" of using one of these, once, in the sixties when some fool accountant mucked up the manual ledger for an entire bank. Yep, a manual ledger. No computers then.

For the young it's calibrated in pounds, shillings and pence. Twelve pence to the shilling in the right hand columns. Nineteen shillings to the pound in the next two. Then up to £999,999,999 after that. Those were the days, eh? We had pecks and bushels, rods poles and perches too. But wait.

What is the other scale on the keys, with numbers going down in value from the top? Does anyone know?