Drag the event P (in S). Slide β = v/c to boost. Top: the overlay view — one shared origin, S′ axes tilt toward the 45° light line, skew read-off. Bottom: S and S′ drawn separately, each with its own axes. Drag any origin dot to reposition.
| ct | 0 |
| x | 0 |
| ct′ | 0 |
| x′ | 0 |
| s² | 0 |
s² = (ct)²−x² is the same in both frames.