We have 2 / 420lb. Propane Tanks that Fuel the Furnace.. Last Dec 21/16 was the First Top of the Season.. I checked the Tank Gauges same day they were topped up, First Tank read 83% , 2nd Tank couldn't find the Needle? Now today as I checked the Tanks , First Tank reads 70%.. 2nd Tank still can't find the needle , was thinking because he went over 80% on the First Tank maybe same for 2nd... Could the Gauge be Faulty?

Sure - do you own them or does the supplier?
Trouble is, the delivery guys all top off at about 80% unless someone wasn't watching, but that's rare. I suppose he could have filled it 100%. It's not a concern like it is in summer.
Also did they write the % on the slip?

@ Joypulv... Their Rentals, a decent Flat Rate charge.. 10-4 on their Responsibility to Fix if need be.. This is the 1st time in 3 yrs the lad has gone over 80% , most times it would be 78%.. Should be good till 1st week of February, Supplier asked that I'd call for Top Ups when Gauges reach 20% each time...

That is standard in the states too.