I've been increasing my lap time by controlling the entry of my hands into the water, less splashy, biggest push at the perpendicular, save your movement to when it moves the most mass.

It's tempting to just go all out and start spraying water like a blender, but that's a waste of energy, ever notice how little splashing olympic swimmers do?

So that's where this comes in. It's a swim cap with a motion sensor that gives you recording of your head movement so you can chart your progress with a pretty big metric for swimming efficiency which equates to speed.

Easier than balancing a glass of chocolate milk on your head. (link)
-- doctorremulac3, Jun 21 2024

Replace the glass of chocolate milk with a sensor. https://www.youtube...watch?v=-foNukLB-5w
The sensor transmits the head movement measurements to your smart watch or phone. [doctorremulac3, Jun 21 2024]

random, halfbakery