The package relevant to Magritte specifically is . This gives you MAMeasureDescription, which represents an Aconcagua Measure. It mostly acts like a number field mapped to its amount. You just have to tell it which unit to use to convert the amount number into a Measure.
label: 'Replacement Price';
unit: AmDollar new;
Then, you can type 100 in a Magritte form and "100 dollars" will be saved to the model. Enjoy!