Digit height is the only number that matters here, and each step roughly doubles the money:
| Digit height | Readable to | Typical use |
|---|---|---|
| 8in / 20cm | about 320 feet | Test and tune, small strips, tower-side displays |
| 15in / 38cm | about 660 feet | Weekly programs with a grandstand |
| 24in / 61cm | about 1,000 feet | Sanctioned events, deep grandstands, permanent installs |
Measure from where the board will stand to the back row of the seating, not the front. A board that the front row can read and the back row cannot will generate more complaints than no board at all.
One more consideration: a single-line board toggles between values, a dual-line board shows two at once. On a bracket program where the crowd wants ET and dial-in together, dual line saves the toggle.