[apalrd]

If you have LabVIEW, I put together a P demo.
You can input a few things:
Gain: This is the tuning parameter
Motor to Movement Scale: How much movement is caused by 1 unit of motor movement (This is for the output, if you had a real robot this would be determined by the gearing and motor load)
Time per Cycle: How fast to run the loop. This will show you what kind of affect loop time has (try tuning it then changing it, it won't work as well).

You can play with Commanded Height and see how Actual Height and Motor respond. There is no sensor feedback, the sensor height is assumed to be what the height was last time (using a shift register).

Maybe if I get some time later, I will add I and D.

Accuracy:
The 10-turn pot will be fine (we have a 12-bit ADC for reference).
You should not expect accuracy greater than 2", less depending on how fast it moves.