H
Hit — the ray strikes an atom head-on and is absorbed. An atom sits straight ahead on that line.
R
Reflect — the ray bounces straight back to its entry. An atom sits right beside the entry port.
1
Detour — the ray bends off atoms and leaves through another port. Matching numbers link the entry and exit.
tap
Tap a port to fire a ray. Tap a cell to mark a suspected atom. Press Check when you've marked all atoms.