No account · nothing saved
Pick a grid size and how many rows to neglect, and see the two numbers that move in opposite directions — how hard you are to watch versus how hard you are to guess. Then try a no-risk round at that size.
Symbol set
Quick sizes
With a single masked field and decoy rows that take any number on the grid, two numbers move oppositely as you neglect more rows (A = active rows, N = neglected, C = symbols):
Hard to watch = C^N — how many different valid digit strings exist, so an onlooker can't pin yours down.
Hard to guess = C^A — the real secret strength against blind guessing.
Each neglected row multiplies "hard to watch" by C and divides "hard to guess" by C. So neglect rows buy watcher-confusion with guessing-strength — exactly the trade you intuit. There's no single best; it depends which you care about. For shoulder-surf-first use, a couple of neglected rows is a strong choice while keeping enough active rows.
At the login screen, guessing is bounded by the lockout (5 tries every 15 minutes). Exhausting the "hard to guess" space would take about — in the worst case — assuming the lockout holds and an attacker can't take a stolen database offline.
These numbers are deliberately modest: PassNumber's job is resisting shoulder-surfing, with guessing-resistance as a backstop. Treat it like a good PIN, not a long random password.
salted-hash storage · single-use board
A working demonstration of the PassNumber method. Your symbols are never stored — only a salted hash is.