Frequently Asked Questions
Answers to common questions about green reading, Stimp ratings, putting physics, and simulator usage. If you have additional questions, feel free to contact us by email.
What is green reading in golf?
Green reading is the skill of analyzing the putting surface — its slope, speed, and grain — before each putt to determine the correct aim direction and hitting force. It accounts for over 60% of strokes lost on the green by amateur golfers, making it the highest-leverage skill to improve in the short game.
What is a Stimpmeter and what does the Stimp rating mean?
A Stimpmeter is a device standardized by the USGA to measure green speed. It is an aluminum ramp from which a golf ball is released at a fixed angle. The Stimp rating is the distance (in feet) the ball rolls on the green. Municipal courses are typically 6-8, tournament greens 11-13, and Masters-level greens can exceed 14. Higher Stimp means faster roll, more break, and the need for more precise reads and gentler pace control.
What is the fall line on a putting green?
The fall line is the direction a ball would naturally roll at any point on the green under pure gravity, with no initial momentum. It represents the steepest slope direction. Identifying the fall line is always the first step in reading a putt because it determines the fundamental direction of break. Putting from above the fall line causes the ball to curve downhill; from below, it curves uphill.
What is the 17-inch rule in putting?
The 17-inch rule, popularized by Dave Pelz's putting research, states that a putt hit with enough speed to finish approximately 17 inches (43 cm) past the cup (if it misses) provides the maximum probability of going in. Too slow and gravity deflects the ball offline before reaching the cup; too fast and the ball rolls past even on a perfect read. This speed provides the optimal balance between holding the line and not blowing past the hole.
What is the Clock Face Method (AimPoint)?
The Clock Face Method is a systematic aiming system used by PGA Tour caddies and AimPoint practitioners. It treats the hole as the center of a clock, with 12 o'clock directly behind the hole from the player's perspective. Instead of vaguely aiming "left of the hole," you communicate precise aim points like "2 o'clock, 6 inches" — meaning aim at a point 6 inches from the hole at the 2 o'clock position. This provides unambiguous, repeatable aim communication.
How does slope percentage affect break?
Slope percentage represents the rise divided by the run, multiplied by 100. A 2% slope means the green drops 2 feet for every 100 feet of horizontal distance. Higher slope percentages cause more break because the lateral gravitational component acting on the ball is stronger. On a Stimp 10 green, a 2% cross-slope might cause 6 inches of break on a 10-foot putt, while a 4% slope could produce over 14 inches of break on the same putt. The relationship is roughly linear at low slopes but becomes more complex at higher percentages.
How accurate is this simulator compared to real greens?
The physics engine is based on peer-reviewed papers by Arnold (2002) and Penner (2002) published in the American Journal of Physics, using RK4 numerical integration. It models gravitational slope components, Stimp-calibrated rolling friction, directional grain effects, and USGA-standard cup capture geometry. While it cannot replicate every micro-undulation of a real green, the fundamental relationships between slope, speed, and break are physically accurate and provide an effective training environment.
Is my training data saved? Is it private?
Yes, all putting records are saved automatically in your browser's localStorage. This means your data is completely private — nothing is uploaded to our servers. You can view your statistics, trend charts, and personal bests on the Progress page. You can also export your training data as a CSV file for analysis in spreadsheet software. Clearing your browser data will reset your training history.
What is grain and how does it affect putting?
Grain refers to the direction in which grass blades grow on the putting surface. On Bermuda grass greens (common in southern climates), grain can significantly affect both speed and break. Putting into the grain (against the growth direction) slows the ball and requires more force; putting with the grain (along the growth direction) makes the ball roll faster. Cross-grain adds a lateral force component similar to a slight slope. Our simulator includes grain angle and grain strength settings to practice reading grain-heavy greens.
Can I share a putting challenge with friends?
Yes! The Challenge feature generates a shareable URL that encodes the exact green conditions (Stimp, slope, distance, and grain settings). When your friend opens the link, the simulator loads the identical scenario. You can compare scores to see who reads the green better. The link is base64url-encoded and safe to share via text message, email, or social media.
Do I need to install anything to use the simulator?
No installation is required. The simulator runs entirely in your web browser using standard web technologies (React, SVG, JavaScript). It works on desktop computers, tablets, and mobile phones. No login or account creation is needed — just open the page and start practicing. The simulator works offline after the initial page load since all computation happens locally in your browser.
How do professionals read greens on tour?
Professional golfers and their caddies use a combination of techniques: visual assessment of slope from multiple angles, feel-based slope sensing (the "AimPoint Express" method of using feet to gauge slope percentage), green maps or break charts provided by course surveys, and accumulated experience with specific grass types and conditions. The Clock Face Method is the standard communication system between caddie and player. Our simulator trains the same core skills — slope identification, break estimation, and pace calibration — in a controlled, repeatable environment.
Ready to Start Practicing?
Open the simulator, set your green conditions, and begin your green reading training journey.