Gateway Tag Change Scripts - Trigger to Script Starting

Hi there,
How do I measure the time took from a tag change on a tag to starting of a Gateway tag change script?
And also does the scan rate for opc tags determines how often a tag will change in value?

You could try looking at the current time vs. the time stamp on currentValue in the script.

The rate is used when subscribing the item on the OPC server. How often it actually changes depends on the load on the server and whether the value is actually changing or not… In theory you should not see changes any faster than the rate, only as fast or slower.