Allen-Bradley 1756-CNB User Manual page 79

Action
6. Keep code as compact as possible.
Details
Avoid checking the same conditions many times. Each instruction adds scan time to your
controller.
This is better
This rung checks Bool_B and Bool_C only once each scan.
Than this
This rung checks Bool_B and Bool_C twice each scan. One or two instructions do not add much
scan time. But if you do this often, the extra instructions add up to a much longer scan time.
Configure and Program the Controller
Publication 1756-UM523F-EN-P - December 2006
79