Function effective_increment 

pub fn effective_increment(
    object: &dyn BACnetObject,
    property: PropertyIdentifier,
    numeric: bool,
    explicit: Option<f32>,
) -> Option<f64>

The increment in use: an explicit one (a SubscribeCOVProperty increment, or a Trend Log’s Client_COV_Increment) wins; otherwise only a numeric Present_Value inherits the object’s current COV_Increment.

The explicit increment is a REAL on the wire; the object’s own may be wider (a Large Analog Value’s Double), so the result is an f64.