B: "Oh, come on -- it's just deciBels referenced to a milliWatt. +30 is one Watt, the power doubles for every 3dB increase, 10 x for every ten dB. Easy."
A: "I'll never remember that!"
B: "Okay, it's basic, just like in school, 10 log (P1/P2), right? And you know the reference is a milliWatt, so all you do is work it backwards, simple algebraic manipulation."
A: Deer-in-headlights look, "But I never took algebra."
B: Slowly, "Divide the power in dBm by 10; raise ten to the result and divide the answer by a thousand, done."
A: Utter panic. "Can't you make us a chart?"
B: Defeatedly. "A chart. Sure. I'll do that."
C: (to A): "Or you could just use a smartphone ap. That's what I do."
A: "What if I don't have my phone?"
B: "What if you lose the chart?"
* * *
The chart is posted -- printed on a self-adhesive plastic label, stuck right above the offending "dBm" readout. Do you suppose they'll catch on that the the "Watts" digits repeat every ten dB with the decimal shifted?
...Yeah, me neither.