Sobel Wiki

The pound is the currency of the Confederation of North America. It is presumably still divided in the traditional £sd manner; certainly shillings were still in use in the early 20th century, when one could watch a movie for a shilling.

It can be assumed that the pound started out equal to its British counterpart. However, high inflation over the course of the 19th century reduced its value considerably. By the 1880s, its value relative to the Mexican dolar had fallen to 80 centavos (p. 221 of For Want of a Nail . . . lists an exchange rate of 5 North American pounds = 4 Mexican dolares). Inflation appears to have slowed down by the end of the 19th century.

Judging by prices mentioned in the late 19th and early 20th century, the pound in 1900 seems to have been roughly equivalent to the US dollar in our timeline, suggesting quite a bit of inflation, as the British pound at that time was valued at US$4.87