SETVALUE

The function will store a value in either a field or a form object on the current form.

SETVALUE(FIELDNAME or TAG // Value)

FIELDNAME or TAG

Either a valid Field name contained in the current forms table OR the TAG value of one of the controls on your form

Value

The value to insert.
NOTE: When setting the value of a CheckBox, 1=Checked, 0=Unchecked

Example#1:
To store the value of 19.89 in the field FIELD1:
SETVALUE("FIELD"//19.89)

Example#2:
To store the value of 19.89 in the textbox referenced by TAG MyText:
SETVALUE(~MyText~//19.89)