Real cheap speedo for 24 inch bike wheel

[professor]

Back before the scrap guys hawked up all the scrap metal, I picked up a couple of exercize bikes - different brands, but both had neat little speedometers on them. Of course, I saved them.
I found this one to be exactly calibrated for the 24 inch mountain bike tire I am running. Used a Schwinn bike computer to check it.
Here is a pic-

 

[shell shock]

hey now, thats a pretty neato speedometer you got there. wanna be a real champ and explain how you got to where you are now?

 

[professor]

Hi Shell, what exactly do you mean?
The bike?
Living in Buffalo?
Frequenting Motoredbikes?

 

[shell shock]

the speedometer. can you snap a pic or two where it meets the wheel?

cheers
shell shock

ps, sorry for the abundant amount of 50s talk XP

 

[professor]

Here you go Shell-

 

[shell shock]

OHH!! ok, now i get it. thanks for your help man, i was picking today (on my new motored bike ^-^) and i came across one of these in a dumpster. now with this knowledge i feel comfortable proceeding with the fab.

cheers
SS