The only way I've discovered so far is to stop and restart the Pico app.
Typically, I connect the physical wires, start the Pico app, then specify the probe options for the particular problem. By the time I'm ready to capture data, there are ~100 buffers of data recorded that I don't need to see.
I would prefer that it record data only when requested or else allow me to say "discard all previously recorded data".
Once the buffer is full it automatically discards the oldest buffer as a new one is captured so you always have x number of the most recent.
If you find that you are finished capturing and still have buffers you don't need, when you save your data, save only the useful buffers. This also has the benefit of reduced file size.
Most people want as many buffers as possible, as Tom says you can choose to only save the one you want. If for some reason you want less then you can go to tools / preferences / general and reduce the no of waveform buffers.
Thanks for the information. I incorrectly assumed that stopping and restarting appends to the logged data. Now I see that the spacebar makes it easy to do what I want.
---rick