diff --git a/640.md b/640.md
index d89bbd9..49cef78 100644
--- a/640.md
+++ b/640.md
@@ -135,7 +135,7 @@ And for a slow speed backwards we can use
 m1.setMotorSpeed(-50)
 ```
 
-##### Alterate speed range
+##### Alternate speed range
 
 If you plan to move from a DC driven robot to an ESC motor powered robot then it makes sense to use the same conventions that will work on both, so you can also use the 1000 to 2000 speed range with the 640 board