Scoring
Chasing Birdies supports scoring in multiple ways:
Standard USGA Rules
Simplified Local Rules
Standard USGA Rules
Everything you've ever wanted to know about USGA handicapping and scoring is located here:
How do I know when I am given a stroke on a hole?
How do I know when I give a stoke?
Simple answer:
The app shows a black dot at the top of the screen whenever you are given a stroke. See image below!
Being "given a stroke" means your net score will be one less than your gross score on that hole. e.g. if it took you 5 strokes to go from tee to cup on that hole, your gross score is 5 and your net score will be 4.
If you are given multiple strokes, you'll see multiple black dots. A maximum of 4 strokes can be given on a hole. A 4 stroke advantage on a single hole means your handicap is at least 55 on 18 holes.
If you are giving a stroke (you are a plus handicapper, i.e. shoot better than par on average), you will see a little red square instead on holes that you give up a stroke.
"Giving a stroke" means your net score will be one MORE than your gross score on that hole. e.g. if it took you 4 strokes to go from tee to cup on that hole, your gross score is 4 and your net score will be 5.
Detailed answer...
A hole index is kept for every hole on every course in the US by the USGA.
Holes on a given course are rated on their difficultly in relation to other holes on the same course.
The easiest hole on an 18 hole course will have an index of 18. The hardest hole will have an index of 1.
A player's course handicap and the hole index is used to determine how many strokes that player is given for that hole, if any
Suppose a player is a 8.8 handicap:
Handicap is rounded to nearest whole digit, with 5 rounding up. This means an 8.8 becomes a 9.
If hole index is between 1 and 9 inclusive, they will get a single stroke on each of those holes
This means the player's net score for the hole will always be one less than the gross score for that hole.
e.g. a par 4 hole with an index of 2 will effectively become a par 5. That player shooting a 5 on that hole will be a net par.
If the hole index is 10 or higher, they will not get a stroke on any of those holes
e.g. a par 4 hole with an index of 11 will stay a par 4. In this case, net score and gross score will match.
Suppose a player is a +1 handicap:
If the hole index is 18 on a par 4 hole, that player will have one stroke removed effectively making that hole a par 3.
If the hole index is 1 through 17 inclusive, that player will get zero strokes. i.e. net score and gross score always match.
What is Adjusted Gross Score? Why is it used in handicap calculations?
Adjusted Gross Score, or AGS, is essentially "limit how high of a single hole score is used when calculating handicap". This is to prevent a single "blow up" hole from wrecking your handicap. It also prevents wild fluctuations in handicap from one week to the next; it "smooths the curve" over time if you plot your handicap from week to week.
AGS is determined under USGA guidelines as essentially the following:
Determine the player's gross score for a hole. Then determine the net double bogey for that hole and that player's handicap and the hole index. The score that is used in handicap calculations for that player for that hole is the minimum of gross score and net double bogey.
AGS for a round is always equal to or less than the gross score.
How is handicap calculated?
This is the million dollar question. Answer is, it's not complex, but it is complicated. There are several factors that come into play:
A history of scores. Multiple methods can be used for selecting which of the scores to include:
Take lowest X of Y
Take middle X of Y
Throw out highest X and highest Y scores, use the rest
Typically USGA recommends the lowest 8 of the most recent 20 scores
A course rating and slope
Courses are judged by the USGA on their difficulty when compared to each other
These result in a Course Rating value and a Course Slope value.
These values will change based on which tees are used and the gender of the player.
e.g.: For Jester Park Golf Course in Granger, IA: https://ncrdb.usga.org/courseTeeInfo.aspx?CourseID=2330
Note there is an entire course rating and slope as well as an independent 9-hole rating and slope. These rarely match, but are always fairly close to each other.
A handicap normalization constant
This is used to level-set handicaps across various regions / climates / etc
A course adjustment
This is used to level-set handicaps across various courses.
= (Avg slope of scores) / 113
Given all that, here's the formula:
handicap = (sum((AGS(selectedScore) - CourseRating) * (113 / CourseSlope)) / # of selectedScores) * HandicapNormalizationConstant * ((sum(CourseSlope) / count(selectedScore)) / 113) - ((sum(CourseRating) / count(selectedScore) - sum(CoursePar) / count(selectedScore))
Simplified Local Rules
The standard USGA method of calculating handicaps is extremely useful when attempting to compare scores from different courses. But what if you are always comparing the scores on a given course? For example, when you're in a league that always plays the same course each week?
This is where Chasing Birdies can let the league choose to follow a much simpler interpretation of the USGA standard. People tend to like the simplicity of this approach, even though it may technically not be as accurate.
Take 5 most recent scores. Throw out the highest score and the lowest score. If only 4 scores exist, throw out the lowest. If only 3 scores exist, use all 3.
No course ratings
No course slopes
No per-hole-index net score calculation
Simplified Adjusted Gross Score (for a single hole) = minimum (gross score, gross double bogey)
aka "SAGS"
Net Score = Gross Score - Handicap
No plus handicaps (always 0 or greater)
Using this approach introduces some difficulties with the standard, specifically -- when do you give / take a stroke if hole index is not used? Simple answer: you don't!
You declare one or more holes as the "net birdie" hole that week.
If you shoot a gross par on that hole, that is considered a net birdie.
Only exception to this is if your handicap is 0; then it is impossible to get a net birdie.
Handicap formula:
handicap = max(0, round(sum(SAGS(selectedScore) - par) / count(selectedScore))