Complex sentence: Moreover, to get the acoustic impedances to match as closely as possible, the mercury had to be kept at a temperature of 40 ° C (100 ° F), which made servicing the tubes hot and uncomfortable work.
Split into simpler sentences: Moreover, to get the acoustic impedances to match as closely as possible, the mercury had to be kept at a constant temperature. The system heated the mercury to a uniform above-room temperature setting of 40 ° C (100 ° F), which made servicing the tubes hot and uncomfortable work.