Killer Wavy Bar Cancel Question???

I was wondering what the numbers in the killer bars represent?
Is it the month or PO Location etc.?

Thanks!

It's simply a machine number. Most of the bigger cities had multiple machines in their main office.

I don't know much about postmarks and was curious. Thanks for the help!

With Cincinnati being a larger city in 1818, They most likely had multiple offices, Office 3, Machine D.

Thank you for the explanation

To amplify a little, this is an International "flier" machine, used widely in large cities across the country starting at the turn of the century and on into the 1920s. There was a smaller variant used in mid-size towns that may have been convertible between electric and hand operation; distinguishable by the length of the killer.

No date on this one presumably because it treated as printed matter. The "D" is a service letter that could be changed to match the category of mail or the process being handled (C = collection, D=deposit, R=received, T=transit) but the letters were as a matter of practice rarely used as intended or, for that matter, changed.

littleriverpihil, no.
Paperhistory's answer above is correct. This is machine 3 at the main office. Machines at stations have the station name as part of the dial or killer.