I had been holding a plastic cup of punch while recording, so the picture wobbled whenever I laughed.

In the video Nathan explained a simple circuit while Zachary interrupted to correct the way he pronounced a technical term.

Then came a moment I hadn’t remembered.

At the end of their presentation Nathan looked directly at the camera and said, “Dad, if you see this, we did it.”

The room went quiet as we watched.

Nathan rubbed his eyes.

Zachary turned away from the screen.