The Less Than or Equal To function compares input A to input B. The function is located on the Compare menu.
If input A is less than or equal to input B: power will flow through the function.
If input A is not less than or equal to input B: power will not flow through the function.

According to the above example:
If MI1's value is less than or equal to MI3's value, then MB 51 will go to logic "1" (ON).
If MI1's value is greater than or equal to MI3's value, then MB 51 will go to logic "0" (OFF).
These values may be compared: