Tips about signal strength metering with percentage
A log scale here feels much more intuitive to the average user than a linear scale, as long as you don't tire them (consumers) with dBm details.

If your range is -100 to -40 dBm, I'd map -100 to a small percentage, say 5% and -40 to 100%. That is assuming you can still receive a signal at -100dBm and you have a separate indicator that your receiver is not locked => 0%

So when locked:
$$percentage = \dfrac{19}{12}×register + 163\dfrac{1}{3}$$

When unclocked: 
$$percentage = 0$$