Thought involves a cloudy rush of neurological activity. For a start, determining where it starts and finishes poses its own problem.
It is not as easy to measure since it doesn't really present itself in a 'physical measurable state' like sound, light etc. Maybe one day, but if you imagine trying to define 'thought' by the time you have thought about the word 'thought' the time/thought measure would have started and ended, over a million times with thinking of the word 'thought' just being one tiny part of the thought process.