Conversions use internationally defined constants where they exist, so the inch, pound, atmosphere and calorie values here are exact by definition rather than rounded approximations. Where units share a name but not a value the tool keeps them separate: mechanical horsepower and metric PS differ by about ten watts, US and imperial gallons differ by roughly twenty percent, decimal and binary storage units diverge increasingly with scale, and thermochemical and IT calories are not the same. Temperature is converted through an absolute scale rather than a simple ratio, which is why a Celsius-to-Fahrenheit conversion involves an offset and why zero in one scale is not zero in another. Fuel economy needs care because miles per gallon measures distance per volume while litres per hundred kilometres measures volume per distance, so the relationship is reciprocal and halving one does not halve the other. Custom units are defined relative to the category base unit and exist only for the current session. For legal, trade or safety-critical work, confirm against the governing standard for your jurisdiction.