How Could You Make a Sensor Unit Conversion Page?
From the earlier reference collection. Read the current software blog.
A trustworthy conversion page displays the formula, input unit, output unit, and rounding policy beside each calculated reading.
Make units part of the input
A conversion page should ask for a number and its unit, then show the converted value with enough context to check the calculation. A bare result such as 68 is ambiguous: it could be a temperature, a speed, or a concentration. Put the source unit next to the input and label the output unit next to the result.
Choose a small set of supported conversions and state the assumptions. For temperature, Celsius to Fahrenheit uses F = C × 9/5 + 32; Fahrenheit to Celsius uses C = (F − 32) × 5/9. These formulas are reversible in exact arithmetic, but displayed rounding means converting a rounded result back may not reproduce the original display.
Show the working
Include the formula in the page near the result, and substitute the entered value in a worked line when that helps. If someone enters 20 °C, the page can show 20 × 9/5 + 32 = 68 °F. The example makes the scale and direction visible. Use appropriate typography for degree symbols and avoid displaying an unlabeled numeric answer.
For a linear conversion such as meters to feet, explain whether the page uses a defined factor and how many digits it shows. Do not imply that extra decimal places make the source measurement more precise. If the source reports one decimal place, converting it to six decimals may be mathematically possible but can suggest unsupported measurement precision.
Handle input and precision deliberately
Validate input before calculating. Reject empty text, non-finite values such as infinity, and units the page does not support. Decide whether locale-specific decimal separators are accepted; if so, explain the accepted format and parse it consistently. Keep the original input visible so a user can spot an accidental unit selection.
Specify the rounding rule, such as rounding to one decimal place for display while retaining the unrounded calculation internally. Boundary cases matter: test zero, negative readings where meaningful, a value near a rounding boundary, and a very large value. For sensor ranges, validation should come from the instrument or dataset specification rather than an invented generic limit.
Keep the result interpretable
Label the result with both the destination unit and a concise formula note. If the conversion is not valid for every context—for example, converting a concentration requires compatible definitions—say what assumptions the page uses. Never infer a missing source unit from a plausible-looking number.
Test each direction with known examples and check that the reverse conversion returns approximately the original input within the display precision. Include an invalid-value state and a clear reset action. A useful conversion page makes the arithmetic transparent enough that a reader can verify it, while keeping the distinction between converted representation and measured accuracy clear.