[basicprofiles] Small improvement to documentation (openhab#18290)

* [basicprofiles] minor improvement to read me

Signed-off-by: Andrew Fiddian-Green <[email protected]>

Author: andrewfg

bundles/org.openhab.transform.basicprofiles/README.md

@@ -242,8 +242,10 @@ The `LHS_OPERAND` and the `RHS_OPERAND` can be either one of these:
   This can be customized by specifying the "window size" or sample count applicable to the function, e.g. `$MEDIAN(10)` will return the median of the last 10 values.
   All the functions except `$DELTA` support a custom window size.
 
-In the case of comparisons and calculations involving `QuantityType` values, all the values are converted to the Unit of the linked Item before the calculation and/or comparison is done.
-Note: if the binding sends a value that cannot be converted to the Unit of the linked Item, then that value is excluded.
+In the case of comparisons and calculations involving `QuantityType` values, both operands, whether they are Item states, the incoming value, or constants, must be of the same type and have compatible units.
+In other words a comparison between a `QuantityType` operand and an incoming `DecimalType` value (or vice versa) will fail.
+All `QuantityType` values are converted to the Unit of the linked Item before the calculation and/or comparison is done.
+So if the binding sends a value that cannot be converted to the Unit of the linked Item, then that value is excluded.
 e.g. if the linked item has a Unit of `Units.METRE` and the binding sends a value of `Units.CELSIUS` then the value is ignored.
 
 The state of one item can be compared against the state of another item by having item names on both sides of the comparison, e.g.: `Item1 > Item2`.