Why are there black dots near the starting scale of some measuring instruments?

The dial of a general indicating instrument is marked with the accuracy level scale of the instrument. The black dot near the starting end refers to the measurement range of the instrument from that point to full scale, which meets the standard level of the instrument. The position of the black dot is generally marked at 20% of the maximum degree value in the table. For example, an ammeter with a rating of 5 amps would have a black dot marked on 1A. It can be seen from some that when selecting an instrument, if the pointer indicates below the black dot during measurement, it indicates a significant measurement error, which is lower than the accuracy of the instrument. In this case, the instrument or transformer should be replaced to keep the pointer between 20% and 100%