HP E4418B Programming Manual page 99

The Condition Polling Method
In this polling method, the power meter has a passive role. It only informs
the controller that conditions have changed when the controller asks.
When you monitor a condition with the polling method, you must:
1. Determine which register contains the bit that monitors the
condition.
2. Send the unique HP-IB query that reads that register.
3. Examine the bit to see if the condition has changed.
The polling method works well if you do not need to know about the
changes the moment they occur. The SRQ method is more effective if you
must know immediately when a condition changes. Detecting an
immediate change in a condition using the polling method requires your
program to continuously read the registers at very short intervals. This is
not particularly efficient and there is a possibility that an event may be
missed.
HP E4418B/E4419B Programming Guide
Power Meter Remote Operation
Status Reporting
1-75