Hi @athw147, The Tobii Pro SDK is part of the Tobii Pro business department.
This forum is intended for support with the Tobii EyeX and C4 Eye Tracker and associated SDK’s such as Core SDK Interaction API.
That being said, I am reasonably certain a value of -1 within pupil size variable represents no data, however I would double
check with Tobii Pro to be sure.
Please get in touch with Tobii Pro Support department directly @ http://www.tobiipro.com/contact/contact-support/ for an
final answer to your query. Many thanks.