Here's what building it taught me.

1. Find the one formula, then stop

A racket's balance point is a centre of mass along one axis. Measure positions in millimetres from the butt cap and every change is a mass at a position:

new_balance = (W·B + Σ mᵢ·pᵢ) / (W + Σ mᵢ)

I spent more time second-guessing this than writing it. Physics already gives you a weighted average, so there's nothing to invent.

2. Inputs are the product

The maths fits in five lines. The work was choosing which inputs players actually understand:

• overgrips as count × grams per grip, not total grams

• lead tape with a position selector, because 5 g at the head and 5 g at the throat feel completely different

• a free "custom weight + position" field for everything else

3. Show a sanity check

People trust a number more once they've seen it move the right way. Some example numbers, using illustrative positions: a 365 g racket at 265 mm with two 6 g overgrips (70 mm) drops to about 258.8 mm. Add a 5 g protector near the tip (440 mm) and you're at about 261.2 mm and 382 g. Grips pull the balance towards the hand and the protector pushes it back.

4. State the limits out loud

The tool computes static balance, not swingweight. Swingweight depends on the moment of inertia, and you need the full mass distribution for that. Saying so up front stopped the first "your numbers are wrong" messages.

5. Skip the framework

It's vanilla JS inside a WordPress page and recalculates on each input event. Nothing to build, nothing to update and it loads instantly.

If you want to see how small a useful tool can be, open the calculator and try your own racket's numbers.