I got one of these a month or so ago from a friend that never used it. Since it has nothing on it at all, how do I get the transponder number? I read something about cloning but I don't understand that either...

Just take it with you to the track and swipe it over the loop and ask the race director what the number is.

Yeah the MRTs come with a piece of paper with the number(s) on it. It's not stamped directly on the transponder. Just hit the loop with it and you'll find out the number ;-)

That's what I had in mind but I didn't know if there was an easier way. Thank you guys!

Just so you have a little more understanding of the MRT transponder:
The cloning of a transponder is done by MRT, which would be transponder number 1. Besides that number, there are 9 or 10 other numbers stored in the transponder. All these numbers normally come on a piece of paper that comes with the MRT transponder. You can change the transponder number by using the button on the transponder. I have never had the need to change the transponder number though....

The first number should be unique. The bonus additional 10 numbers you can switch to are always the same on every MRT. So you can cross the loop to find your unique number and ask around to see if anyone saved their paper sheet to see your other numbers.

PTX Number SET ONE
"Flash" (1 to 10)
ID:1 = 4961721
ID:2 = 3519622
ID:3 = 6091953
ID:4 = 5640314
ID:5 = 4572215
ID:6 = 7531106
ID:7 = 2351957
ID:8 = 2688158
ID:9 = 3073479
ID:0 = 5564690

PTX Number SET TWO
"Flicker-Flash" (1 to 10)
ID:1 = 9887001
ID:2 = 7621202
ID:3 = 6000513
ID:4 = 8110984
ID:5 = 5843805
ID:6 = 8087916
ID:7 = 4748687
ID:8 = 6099608
ID:9 = 5781589
ID:0 = 9577130