Ionizing radiation is subject to major statistical variations in this area of brief measurement. Only a few pulses are measured over a period of minutes and converted into dose. You want to take a quick reading and not wait for, say, an hour in order to avoid these variations. The “average daily value” (activity symbol) eliminates short-term variations or you can switch to daily or weekly figures to establish that the underlying figure is extremely stable.
(Prof. Dr. Erich Foßhag, Mannheim University, Faculty of Process and Chemical Technology, Institute for Physical Chemistry and Radiochemistry).