Golf Rules Report V2
R&A / USGA / JGA Rule 4.3a(1) Explained Where "Prior Notes" End and "Real-Time Information" Begins
Research sections
1. DMD rules & prior notes
Measuring straight-line distance between two points is allowed; measuring "what is happening right now on the spot" is not.
Past data & handwritten notes: OK
The rules do not restrict using information obtained before the round. The following "handwritten notes" are permitted even if recorded on a yardage book or DMD screen.
- ✔Wind tendency or elevation notes from practice rounds up to the day before
- ✔Club-used records for the hole from past stats
- ✔Green lines copied from TV or past data
Straight-line distance
Distance from your position to the flag.
Slope-adjusted distance
Display of "distance to play" with slope.
Prior notes
Wind or club notes recorded before the round.
Live wind measurement
Real-time wind speed measurement.
Score recording
Digital scorekeeping.
Club recommendation
Auto club suggestion by distance.
2. Digital "real-time" risk
The real-time trap
Having an app on your phone alone is usually not a breach. Activating a function that obtains "current values at that location" is a breach.
Safe (allowed)
- ・General weather forecast (broadcast / wide-area)
- ・Pre-downloaded course map viewing
- ・Reviewing your own past shot data
Out (breach)
- ・Wind meter app measuring wind at current location
- ・Phone level app for slope measurement
- ・Real-time wind overlay on course map
3. Common violation factors
Modeled from main penalty causes in competition (2019–2024)