Isohold

Static muscle strength is foundational in many precision sports.
Isohold uses motion detection to help you train your arms' isometric hold. Used with or without wrist weights, it allows a target shooter to improve stability of their hold after a lift or transition.
An excellent companion to your routine practice! Use Isohold anywhere you have your phone with. Just a few minutes per day to make a difference. The difficulty level can be adjusted separately for shake and twist of your grip.
Adjust the difficulty, hit the button, and do your best holding the device after 3 second countdown! You'll know the round is completed when the phone buzzes and vibrates in your hand. The app then will show your time.