@Wayne-TP thanks for yor reply Wayne. Unfortunately the attached screenshot shows that the measured power of 6W has not been updated for 10 minutes, not 5. It would be great if the plot update was every minute or even every second, since the power in Watts is updated in real time. That's the reason I bought the Tapo, instead of using my existing (non power measuring) Meross sockets.

  @Wayne-TP yes, I had to switch back and fourth to even update the plot, and apparently data points are only at 5 minute intervals, as you say. So power plotting is only useful over long periods with the current app software, though clearly the plug measures the power in real time and real time plotting should be possible to code. Even without real time plotting, increasing the update rate from 5 minutes to 1 minute (or ideally to a user selected interval) should be easy to code, and would be very useful. But I guess that's not going to happen any time soon, so I should explore alternative devices. Thanks again for helping me understand. Alan.

  @Wayne-TP thanks again Wayne. Yes, data export is quite useful and clearly shows intervals of 5 minutes (fig. below). Here I was charging a battery power bank at 13W; the table and plot shows the smart battery gradually reducing it's power consumption  to zero as it approached full charge. I had set a Tapo Power Guard to switch off after <2W for 1 hour, and that is also quite useful. I also limited the Tapo  maximum Power Protection to 45W, since that is the limit of my USB-C charger, which gets quite warm at full output for long periods.

So Tapo recording was useful for understanding power usage by my battery and laptop over long periods, though I would have liked a finer time interval. I can visually see the power in real time, but I can also do that with a mini USB power meter, though I can't record it in real time as I had hoped.

  @Wayne-TP thanks for the suggestion Wayne. I have voted for that, and added the following comment.

It would indeed be great if the time interval for recording could be user set. At present the power (W) is recorded every 5 minutes, but for many applications a granularity of 1 min or even 1 sec would be useful. Power plot updating in real time would also be useful. For example, monitoring the power delivered to my laptop computer with various loads to maximise battery use. The only alternatives are USB meters, which don't record, and other brand plugs, that don't do it either. That would be a unique advantage for Tapo plugs.