I've been using the Ketonix for about 2 weeks but I haven't done any 'fasting calibrations' yet. My measurements have averaged around 60 within a range of 45 to 70, except for one occasion when I tested the effect of alcohol by drinking a single glass of italian merlot. This is shown in the chart below by the spike to a reading of 85 on 6July. The Ketonix manual explains the following about the effect of alcohol:

Acetone is a byproduct of the breakdown of alcohol and can result in a positive measurement. Whilst your body is processing alcohol ketosis will be put on hold until it is gone. We recommend not to drink prior to carrying out a measurement.