It's a feature of the way the anemometer is constructed. 0.7 mph is approximately the minimum speed that it can measure, and it will only ever display approximate multiples of that. It measures in m/s, so the odd values you see are a result of conversion to mph and a rather strange rounding algorithm. The speeds you will see are 0, 0.7, 1.6, 2.2, 3.1... mph. So the console can display speeds to 0.1 mph, but the anemometer itself does not have that level of resolution.