Originally Posted by Joey

If you multiply the resistance by capacitance you will get the frequency in milliseconds, , the charge or discharge time remain constant.

EG: if you pick a 1uf cap for C1 and 100 Ohm resistor for R1 it will be 100 x 1 = 100ms meaning your output will flash 10 times per second.

So if you want it to flash once per second you change R1 to 1K or 1000 ohms.

If you were to put a wire link across R1 you would need a 1000uf cap to get the same 1 second pulse.
But if you added a 1K resistor using the same cap it would be 1000 x 1000 about 16.6 minutes per pulse. this is where these IC's become good timers.

Basically if you use a 1uf cap for C1 and a 5K variable resistor ( pot ) for R1 you will be able to play quite a bit with frequencies that are visible via a led on the output.