We can define a number field thereby converting the value being set into Number Type and using Format Specification.
Example
[Field: TSPL Sample Field]
Use: Number Field
Set as: $$Number:($$String:$BilledQty:Symbol,ShortFrom,Secondary)
Converting BilledQty into String is needed as Format Secondary will work only if the value is of Type String. Hence, converting Quantity into String and subsequently, into Number to extract only the Number component out of it.