Using only the DC1 reading on the Digatron fuel tester is not a wise thing to do, as we have found out that many teams or individuals are mixing fuels or adding additives to MAKE it fall within the range on DC1 that tracks are allowing. The Digatron instruments are designed to give a specific reading on various fuels when the instruments are calibrated with either cyclohexene, 100 octane aviation fuel or xylene (-75,-93,-5). All gasoline's will have a different reading on DC1 but on DC2 all should test 0 +/- 1.
You can specify based upon purchases from a single gas station a range that DC1 must fall within and be fairly accurate unless you have those who are mixing fuels to get within your level, the DC2 test will detect those who are doing this.
87 octane with up to 10 ethanol will test a lot less negative than 97 regular without ethanol, 89 and higher octane fuels contain less ethanol than 97 octane with ethanol and will test more negative than 87 octane(with 10% ethanol).
All grades of gasoline should still test 0 +/- 1 on DC2 unless other than normal additives are added to it. Having worked in a calibration lab for years both calibrating instruments and strandards we decided years ago that on digital readouts you had to give an additional +/- 1 count to any tolerance that you allow so in this case I would say any reading other than 0 +/- 2 on DC2 tests would be questionable .
Even through temp of fuel being tested should be measured in most cases it makes only a slight difference on both the DC1 and DC2 tests but should be considered before making a DQ.
Here is one thing that I have noticed on making fuel tests:
If most karters at an event fall with say a reading of -28 to -35 on DC1 and on DC2 0,+/- 1 and some have a reading of -20 or less on DC1 and they show -3 on DC2 ,during tech the carbs most likely will have a jet size bigger than the others, say 42 vs everyone else 38/39.
The new Digatron 60 Series Fuel tester has a 4 window viewing area all at once, it shows DC1,DC2 fuel temp and a self check window. The instrument probe is a lot more sensitive than previous models. If I had both models then what I would do is calibrated the New DT60 with one of the three known substances that we have listed on both DC1 and DC2, then calibrate the DC47 or other fuel tester to read exactly on DC1 what the DT 60 reads on a known fuel. Then I would use the Dt47 to make most checks on competitors fuels and if any are close to be questionable make a final test with the DT60, especially on DC2.
Many techs/tracks have been calibrating their fuel testers by just buying a fuel from a station and giving so many points from that reading or adjusting the DC1 to zero and giving so many points, this actually is not a good procedure with what is going on now with karters mixing fuels and buying their own fuel testers. The DC 2 tests need to be done to even the playing field and calibration of your meter against one of the three fluids that we recommend. You can still give a range on DC1 which will compensate for the stations not having pure 87 octane because the fuel supplier was short on 87 and filled the order with some 89 or higher octane.