Letter: Formula for converting water temps needs to be adjusted

In last week’s article about the frustration expressed by Peter Van De Carr, owner of Backdoor Sports, over the city’s closure of the Yampa River to tubing, the Steamboat Pilot & Today reported that the city uses a thermometer capable of measuring the water temperature to the tenth degree Celsius. The city closed the river when the water temperature was measured at 23.9 Celsius two days in a row, claiming that those measurements exceeded the 75 Fahrenheit maximum temperature allowed for tubing.

The city is mathematically wrong on this account. According to the rule of significant digits, any digit beyond the most significant digit of the item measured is “insignificant” and must be disregarded. To convert from Celsius to Fahrenheit, one multiplies the Celsius number by 1.8 and then adds 32. True, that formula technically produces 75.02, or “above 75 degrees Fahrenheit. But, since the Celsius measurement is only accurate to a tenth of a degree, the mathematical conversion to Fahrenheit is only accurate to (at best) a tenth of a degree.

Consequently, the resultant conversion must be rounded to 75. Stated differently, if the water temperature had been measured by a Fahrenheit thermometer accurate to a tenth of a degree, it would have registered 75.0 Fahrenheit. It is inaccurate to assert that the Yampa “exceeded” 75 Fahrenheit based on a Celsius reading of 23.9.

The river should not be shut down until Celsius measurements of 24 degrees Celsius or higher are recorded.

Colin P. Cahoon

Steamboat Springs

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