Fixing singal strength docs and adding an example (#347)

docs/reference/radio/on-data-packet-received.md

@@ -21,7 +21,7 @@ To add or remove the parts of the packet from the block, try clicking the blue g
   * `receivedString` - The [string](/reference/types/string) that was sent in this packet or the empty string if this packet did not contain a string. See [send string](/reference/radio/send-string) and [send value](/reference/radio/send-value)
   * `time` - The system time of the @boardname@ that sent this packet at the time the packet was sent.
   * `serial` - The serial number of the @boardname@ that sent this packet or `0` if the @boardname@ did not include its serial number.
-  * `signal` - How strong the radio signal is from `255` (weak) to `0` (strong).
+  * `signal` - How strong the radio signal is from `-128` (weak) to `-42` (strong).
 
 ### Example
 
@@ -39,6 +39,23 @@ radio.onDataPacketReceived(({ receivedNumber }) => {
 })
 ```
 
+### Example
+
+This program uses the signal strength from received packets to graph the
+approximate distance between two @boardname@s.
+
+```blocks
+basic.forever(() => {
+    radio.sendNumber(0)
+})
+radio.onDataPacketReceived(({ signal, receivedNumber }) => {
+    led.plotBarGraph(
+        Math.abs(signal + 42),
+        128 - 42
+    )
+})
+```
+
 ### See also
 
 [send number](/reference/radio/send-number),