Thanks Benno, that seems to be the case. I've just opened the file in Notepad++ instead of Excel and I see that the mystery data is read as -∞ in Unicode.

I am having an issue with exporting data to CSV where some data comes out as seemingly random characters, as seen in the attached Excel screenshot. This makes processing and plotting results using other software tools difficult or impossible. For reference, the equipment used is: PicoScope 2406B har...