Use this when you need to convert a value between units within one category (length, weight, temperature, volume, data, speed, area, time) instead of doing conversion arithmetic yourself.

Use this when you need to convert a value between units within one category (length, weight, temperature, volume, data, speed, area, time) instead of doing conversion arithmetic yourself. Deterministic: same input, same output. Temperature uses the correct offset formulas (Celsius/Fahrenheit/Kelvin), not a naive ratio, and unit keys are case-sensitive (e.g. km, lb, celsius, MB) while the category name is case-insensitive. Example: {category:'length', value:5, from:'km', to:'mile'} -> result 3.10685596119. Returns the echoed category/value/from/to plus the converted result, rounded to 12 significant figures (switching to exponential for very large or very small magnitudes).