I have full set of hydrometers for nitro and one for alky. That is how I know they read same.The nitro set I have electric thermometer also. After reading hydrometer,reading temp and going to chart I found out it was 40$ the proofing hydrometer read 70& alcohol, meaning 30% nitro. I did this with three different mixtures and all checked the same. Never said it was 100% replacement. It is a quick check