I believe that is backwards. Full deflection (full) should be when the resistance is the lowest so 10 ohms or less should indicate full.
80 ohms is when the tank is the lowest.
As for size of resister, at full, you need at least a 2.5 Watt resistor. You are drawing a half an amp at 5 volts through 10 0hms. Power = I squared times R or .25 X 10 = 2.5 watts.
Easier still, use this web site to calculate it all out:

http://masterslic.tripod.com/olcalculator.html

Craig