One application of the use of radioactive materials of particular interest to westerners, especially those who live near rivers, is radio cobalt. It is used to measure the depth of snow in the Sierra Nevadas. For some years, a group of cooperating agencies has taken measurements of the snow-pack throughout the range. This required trips on snowshoes and skis by snow surveyors. The radio cobalt station now being tested at the Sierra Nevada Snow Laboratory may do away with most of this hard work. A tube of radio cobalt is placed at ground level and its signals are picked up by a detector directly above it. As snow piles up, the strength of the signal decreases with the quantity of water stored in the pack. Theoretically, a network of these installations would make it possible to keep an accurate record of the snow depth from one central station.

Q. Underline the sentence which implies that keeping accurate records of snow depths has not been easy work.