I use a Casio "Wave Captor" for my projects needing very accurate timing (Its an atomic watch anlog and digital with about the most accurate timing you need)
I used to use my cell phone but I always either had to hold it or lay it on the drill table or pump arms and it was hard to read. A watch is still the way to go for scienceneeds (other than a built in atomic clock on your equipment)
Its accurate to one second in 80 000 000 years.
I also have a Tag Heuer chronograph. Its accurate but not as easy to operate as the Casio aAND its not an atomic watch.
An atomicwatch is the same timepeiece that's sent to your smart phones