Adding temperatures in rule script gives unexpected results

[rossko57]

Work with Quantity types.

Working with Number:Temperature Items in rules

openHAB provides Quantity Type features, which can seem baffling. On top of that, Temperature type Quantities have a few quirks all of their own. These notes intend to guide the rules author. I’ve shown work examples in DSL rules language, see below for other scripts examples. All have similar features, if different syntax. Knowing what can be done is half the battle. What is a Quantity Type? Simply, Item states and rule variables may contain Quantities - that just means a number AND a unit …

The cause of your problem -

@hdr_jgrade

var setpoint = Upstairs_Setpoint.state as Number

yields a number with units, but this does not behave like a true quantity type in computations.