The temperature lost along the umbilical in Fahrenheit, from its length in feet and the flow in US gallons a minute.
The formula: Drop (F) = length (ft) / (5 x US gal/min). Change any box and the full working updates. For study only, never for dive planning.
The IMCA ADS, BDS and LST papers ask this as a four-option question, with a calculator on screen. A free account gives you 15 practice questions for each exam, each with the worked answer and the document it comes from.