Multiply – a book about calculators I helped create

> "a book about (calculators THAT I helped create)"

> "(a book about calculators) WHICH I helped create"

https://en.wikipedia.org/wiki/Checkwriter#Machine

> A check writer, or ribbon writer, leaves a numerical or written value impression in the payment amount field of a check that is very difficult to alter. This is accomplished by the machine applying downward force on the check and leaving very small inked shreds in the paper.

> The first check protector was introduced in 1870. The best known check protectors in the early 1900s had the brand name Protectograph (the Todd Company, Rochester, NY). Other well known manufacturers in the industry were F & E Hedman and the Paymaster Company (both out of Chicago, IL).

> The person preparing a check positions the check in the check writer so its print-heads are centered over the field on the check where the amount of the check would otherwise be written out in words. Using a series of levers or buttons on the checkwriter's control panel, the operator enters the monetary amount of the check. This amount is then printed onto the check by the operator pulling a lever on the side of the unit (or by pressing a button on electric units). This brings the print-heads down upon a wide inked (usually multicolor) ribbon through which they print the selected amount on the check, with a prefix and suffix to prevent a fraudster from adding extra digits. Entering $6,762.64, for example, will produce text reading "TheSum6762dol's64cts".

> There is a series of (usually) horizontal indentations on a pressure bar brought up underneath the check during this process, which matches similar indentations on the print-heads. This embosses the numeric amount through the paper of the check form, strongly discouraging any attempt to alter or raise this amount.