Cellular backhaul networks usually consist of commercial microwave links, known to be sensitive to weather conditions. The management network systems usually provide records of measurements of the transmitted and the received signals levels from the different microwave links for monitoring and analyzing the network performance. Many of them log only the minimum and the maximum levels of the transmitted and the received signals in pre-set intervals (usually 15-minute). Moreover, only quantized version of these measurements are logged. In the last decade it has been proposed to use these existing measurements for rainfall monitoring. In this paper we analyze the effects of the quantizer and the min/max operators on commercial microwave links signals levels measurements. We show that the quantization process, in combination with the min/max operators, adds bias to the measurements which can be significant. We then propose a method to calculate this bias, and demonstrate our findings using measurements from actual commercial microwave links.