Download and print the Windows Alternate Character Set table and keep it handy on a clipboard near your computer as a cheat sheet. You need a keyboard with a right-side number keypad and a NUM LOCK key. Once NUM LOCK is on, just leave it and it will allow the alternate character set to be entered by holding down the ALT key and typing the two, three or four numbers from the table.
I use it a lot for foreign business correspondence. It has the principal currency symbols like €, £, and ¥, and all the math symbols. For PM, ° and Ø are useful.