Add the 'strength' option to the acceleration doc page. (#527)

docs/reference/input/acceleration.md

@@ -1,6 +1,6 @@
 # Acceleration
 
-Get the acceleration value (milli g-force), in one of three specified dimensions.
+Get the acceleration value (milli g-force) in one of three dimensions, or the combined force in all directions.
 
 Find the acceleration of the @boardname@ (how fast it is speeding up or slowing down).
 
@@ -15,15 +15,17 @@ A **g** is as much acceleration as you get from Earth's gravity.
 
 ## ~
 
-
-
 ### Parameters
 
-* ``dimension`` means which direction you are checking for acceleration, either `Dimension.X` (left and right), `Dimension.Y` (forward and backward), or `Dimension.Z` (up and down)
+* **dimension**: the direction you are checking for acceleration, or the total strength of force.
+>`x`: acceleration in the left and right direction.<br/>
+`y`: acceleration in the forward and backward direction.<br/>
+`z`: acceleration the up and down direction.<br/>
+`strength`: the total of all the forces in every dimension (direction) together.
 
 ### Returns
 
-* a [number](/types/number) that means the amount of acceleration. When the @boardname@ is lying flat on a surface with the screen pointing up, `x` is `0`, `y` is `0`, and `z` is `-1023`.
+* a [number](/types/number) that means the amount of acceleration. When the @boardname@ is lying flat on a surface with the screen pointing up, `x` is `0`, `y` is `0`, `z` is `-1023`, and `strength` is `1023`.
 
 ### Example: bar chart
 
@@ -34,7 +36,16 @@ basic.forever(() => {
     led.plotBarGraph(input.acceleration(Dimension.X), 1023)
 })
 ```
+### Example: quake meter
 
+Every 5 seconds, with the @boardname@ facing upward on a flat surface, show how much the earth is shaking (if at all).
+
+```blocks
+basic.forever(() => {
+    basic.showNumber(input.acceleration(Dimension.Strength))
+    basic.pause(5000)
+})
+```
 
 ### See also