Of course, there is no guarantee that Astley is correct, either--I've found a couple errors in his book. However, it seems clear to me that the 22 ohm resistor is right, and the 150-ohm pot could be OK. If you have 50, and it hits the stops before you can get the tach to read the right value, just add another resistor of 50-100 ohms or so in series with it.