If you’ve ever stood over an 8-footer thinking “that’s definitely going to break right” only to watch it slide three feet past on the left you already know the most painful truth in golf: the stroke usually isn’t the problem. The read is.
There’s a new iPhone app that attacks that problem head-on. It’s called Plumb Bob, it’s called that for a reason, and right now GolfProblems.com readers can try a full year of it for a fraction of the normal price (more on that below).
What Plumb Bob Is
Plumb Bob is a golf green reader for iPhone. You scan the green with your phone’s camera on the walk you already take from ball to cup, and the app measures the actual slope along your entire putting line not just the patch of grass under your feet. Then it draws the answer right on the grass through the camera: the line, the aim point, and how much the putt breaks.
Every read gives you the four things a good caddie would tell you:
- AIM — where to start the ball, in inches left or right of the cup, with an aim spot marked on the grass
- BREAK — how much the putt curves, in cups, the same way you’d call it to your playing partner
- PLAYS-LIKE — uphill and downhill converted into real distance, so an 11-footer that plays 12 gets hit like a 12-footer
- MAP — a top-down view of the slope under your putt, with a confidence rating so you know when to trust the read
The Oldest Trick in Golf, Finally Done Right
Plumb bobbing is a green-reading technique that’s been around for about a century: hang your putter shaft vertically in front of your dominant eye, line the bottom up with the ball, and see which side of the shaft the hole falls on. The problem and it’s a big one is that the method only works if the shaft is truly vertical, your stance is square to the slope, and the slope is the same at your feet as it is all the way to the hole. In real life, it almost never all holds at once.
Plumb Bob keeps the part that works and kills the guesswork. Your phone knows exactly where straight down is, and the walk to the hole maps the slope along the whole line. The app then rolls simulated test putts across that surface at your green speed and shows you the one that actually drops.
It Even Measures Green Speed Without a Stimpmeter
Break depends heavily on how fast the greens are running, and most of us have no idea what a given green stimps on a given morning. Plumb Bob handles it: roll any ball 8 to 15 feet across the green and the app tracks it with the camera, calculating the Stimp from how quickly the ball slows down. Roll one back the other way to cancel out slope. Don’t want to roll? Pick Slow, Medium, Fast or Tour from a preset.
Practice With a Score Attached
Here’s the part that turns this from a gadget into a training tool. Start a round in the app, log your putts, and every one gets scored against a PGA Tour putter from the same distance real strokes gained putting, for your own rounds. The stats view then shows where you’re bleeding strokes: make percentage by distance versus tour, left breakers against right, uphill against downhill, and a single specific thing to work on the next time you’re on the practice green.
Getting Started Couldn’t Be Easier
Three full reads are free no account, no credit card. Everything is computed on your iPhone, so it works even with no signal at the course, and nothing about your putts ever leaves your phone. It runs on any iPhone with iOS 17 or later; Pro models with LiDAR get the most precise reads.
One honest caveat the developers are upfront about: under Rule 4.3 of the Rules of Golf, you can’t use a device to measure green slope during a competition round. Plumb Bob is built for practice rounds, lessons, and friendly games which is exactly where a bad read is costing you the most reps.
The Deal for GolfProblems.com Readers
Plumb Bob Pro normally runs $59.99 a year (or $9.99 a month, with a free first week for new subscribers). But readers of this site can get their first year of Plumb Bob Pro for just $24.99 a 58% discount.
- Code:
GOLFPROBLEMS - Price: $24.99 for the first year (regularly $59.99)
- Who it’s for: new subscribers
- Valid through: December 31, 2026
Download Plumb Bob from the App Store and enter the code at checkout to lock in the discount.
The Bottom Line
You can drill your stroke all winter, but if you keep starting good strokes on the wrong line, three-putts will keep finding you. Plumb Bob takes the oldest read in golf, removes the guesswork from it with your phone’s sensors, and tells you exactly where to aim then scores your putting like a tour caddie would. For the price of a couple of sleeves of balls, the first year is an easy bet for anyone who’s ever blamed the read.
Plumb Bob is available on iPhone (iOS 17+). Prices in US dollars; your App Store may show local pricing.