A VI which shows the differences between using a control/indicator, local variable and value property node to update a value.
When updating a graph you may need to position two cursors, change some colors, and write the data to the graph. In older versions of LabVIEW, this required two nodes: one for properties and another (Local Variable or Indicator) for the value. This resulted in two graph redraws. However, using a Value Property Node on the existing node instead of a Local Variable or Indicator will result in one less graph redraw, improving the performance of the code.
For controls that are updated very quickly (i.e. more than 50 times a second) Local Variables and Indicators have built in logic to alleviate and reduce the redisplays to save CPU cycles that would otherwise be spent redrawing objects unobservable to the human eye. The VI Snippet below will demonstrate the performance benefit of using a local variable instead of a property node for quick updates.
Steps to Implement or Execute Code
Run the VI and you will notice the loop that updates the property node will run slower.
If you want to force Indicator Update to update the front panel on every iteration, you can right-click Indicator Update and select Advanced>>Synchronous Display.
Run the VI again, and you will notice now that the loop writing to Indicator Update takes longer to complete.
LabVIEW 2012 and later
Additional Images or Video
Paolo F. National Instruments Applications Engineer