From my very limited experience, I have seen 20s - 60s, and given that in car antennas attenuate significantly compared to roof-top antennas, and that signals are going to be far lower in the city/mountains than in the plains/desert, maybe displaying 20-68 would be a better solution...ie subtract 20 and divide by 2.

Just a thought.
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Mk2a 60GB Blue. Serial 030102962 sig.mp3: File Format not Valid.