Added Arithmetic commands examples

Rules.md

@@ -272,8 +272,59 @@ Note that the following won't work:
 
 Well at least not as you probably would expect. The var1 value used by the power1 command will be the value present before the backlog command is executed. This is so, because the rule will replace %var1% BEFORE the backlog commands are put in the backlog-log.
 
+#### 8. Arithmetic commands to be used with `VARs
 
-#### 8. Simple Thermostat Example
+* ADD
+
+`ADD1` to `ADD5`: Add a value to `VARx`
+Syntax: `ADDx value`
+Usage: `ADD1 15`
+Result: `VAR1 = VAR1 + 15`
+
+* SUBSTRACT
+
+`SUB1 `to `SUB5`: Substract a value from `VARx`
+Syntax: `SUBx value`
+Usage: `SUB1 15`
+Result: `VAR1 = VAR1 - 15`
+
+* MULTIPLY
+
+`MULT1 `to `MULT5`: Multiply a value to `VARx`
+Syntax: `MULTx value`
+Usage: `MULT1 15`
+Result: `VAR1 = VAR1 * 15`
+
+* SCALE A VALUE
+
+`SCALE1 `to `SCALE5`: Scale a value from a low and high limit to another low and high limit and store it in `VARx` (directly equivalent to MAP arduino command)
+
+Syntax: `SCALEx value, fromLow, fromHigh, toLow, toHigh`
+
+where,
+
+_value_: the number to scale
+_fromLow_: the lower bound of the value’s current range
+_fromHigh_: the upper bound of the value’s current range
+_toLow_: the lower bound of the value’s target range
+_toHigh_: the upper bound of the value’s target range
+
+_(omitted values are taken as zero)_
+
+Usage: `SCALE1 15, 0, 100, 0, 1000`
+Result: `VAR1 = 150`
+
+* Example: Sending the value of a sensor to MQTT only when a delta is reached
+
+When it is needed that a sensor value is only sent when it changes a delta, can be solved applying the following rule example:
+
+```
+rule
+on AM2102#temperature>%var1% do backlog var1 %value%; publish stat/sonoff/temp %var1%; var2 %var1%; add1 2; sub2 2 endon
+on AM2102#temperature<%var2% do backlog var2 %value%; publish stat/sonoff/temp %var2%; var1 %var2%; add1 2; sub2 2 endon
+```
+
+#### 9. Simple Thermostat Example
 
 As example, to be used on a Sonoff TH10 with Sensor Si7021