the calculation is using a ternary expression.
a ternary expression is a shortened if statement using the following format:
expresion?true statement:False statement
in other words, this statement:
abs([Quantity] == 1)?[ItemHeight]=8:[ItemHeight]=14
Quantity == 1?
yes: Set the Item Height to 8
No: Set the item height to 14
the height be set to 14 if the quantity is anything other than 1. Set the quantity to 2 or 3, the height will be set to 14