In PTC Mathcad Prime, you can customize how units are handled by creating your own unit system. While PTC Mathcad Prime provides three standard unit systems—SI, USCS, and CGS—you have the flexibility to define a fourth option, called a Custom unit system. This allows you to tailor the units used in your calculations to match your specific requirements.

To set a custom unit system, select one of the three built-in unit systems as the foundation for your custom setup. From there, you can adjust it by choosing your own base and derived units. For example, you can replace meters with inches as the default length unit while keeping other units unchanged, like kilograms for mass or seconds for time.

When you create a custom unit system, you control the simplification rules. These rules determine how results are expressed in terms of units. For example, if you want PTC Mathcad Prime to automatically simplify 1/s to Hz, you can add Hz to your list of derived units. Any result that has dimensions of 1/s is automatically displayed as Hz. You can also remove simplification rules, so the result remains in base units. You can have as many simplification rules as needed, even though one rule may override another. The last rule applied takes precedence.

While you have a lot of freedom in choosing and defining units, you cannot remove the core base dimensions like length, mass, or time, as these are required for any unit system. Also, functional units (DMS, FIF, and hhmmss) or scaling units for temperature (°C or °F), are not available — you can use only multiplicative units for default simplification.