AW @ Anton Paar

These are almost certainly maintenance and adjustment issues. First rinse the cell with a warm 1% caustic such as Alconox (amazon) and let it set 3-5 min then flush thoroughly with distilled water (grocery store) ....and then flush again and again. Wait at least an hour, then perform a water check. If fails, try again. If you are certain the cell is clean, follow the prompts to perform an adjustment. Run a major brand stripped vodka and should be very close. Triple Platinum is sold everywhere, I believe, and will measure 40.00 %v/v (using Ethanol AOAC @ 60 K method). Run water checks daily (min). You should only need to adjust the instrument (with distilled water) a few times/yr (which is why many stop checking). My DMA has been hit by a forklift and traveled many miles in my truck bed and always measures right-on. I use many of our customer's brands basically as standards. They almost all bottle at slightly different proofs, but they are always the same, or will be on a properly maintained DMA.

Very biased opinion here; I've been really impressed with the Alex 500 for spirits. It was originally designed for beer and wine but recently upgraded to also measure spirits. There will be obscuration for heavily flavored spirits, but measurements are typically very repeatable. Some samples may need filtration beforehand for any undissolved solids. You can go here for a quote: https://www.anton-paar.com/us-en/products/details/alcohol-and-extract-meter-alex-500/ Your local rep will follow up and they can arrange for you to see it.