Arduino Starter Kit Project 07 - modified
The original project 07 had too large a resistor, which made the circuit unreliable. This circuit shows a simple fix.
I replaced the 1MOhm resistor in the original circuit with a 30KOhm resistor. Actually by 3 10K resistors because the kit contains several 10K resistors.
The original circuit's 1MOhm resistor produced input voltages that were often indistinguishable from zero. I calculated the appropriate resistor value to produce an input value half way between 0 and the value from the next button.