typed Alt-246. Press and hold the Alt key while you type 2 4 6 on the numeric keypad, not the numbers across the top of the keyboard. You need to have Num-lock on.
I use this most often to insert the degree symbol, which is Alt-248: °
Another useful one is Alt-241, which is the plus or minus symbol: ±
These are extended ASCII codes. They work on a PC. There is something similar on a Mac, but I don't know what it is. You could look it up on the internet.