Privacy & how it works

NumberSense on the web is built the same way as our iOS apps: private by design.

Everything stays on this device

Your progress, your estimates, and your calibration card are stored only in this browser (on-device storage). Nothing is ever sent anywhere. Clear your browser data and it's gone; nobody else can see it.

No accounts, no ads, no tracking

There is no sign-up and no login. There are no ads and no in-app purchases. There are no third-party trackers embedded in the app.

How it works

The heart of NumberSense is estimating first: read a real-world prompt, lock in a gut guess before you calculate, then work out the answer and see how close you were. Over time your calibration card shows whether you guess high or low and how your number sense sharpens. You can also place numbers on an open number line, choose the mental-math strategy that fits a computation, and flash-read quantities without counting. There is no "wrong" — every guess-then-check makes your feel for numbers stronger.

Meet the cast

Estimator Ernie, Splitter Sasha, Ratio Rio, and Pivot Pia each carry a piece of the estimation posture. Read their stories →