Callaway is a popular scoring system used for onetime events where a number of competitors don't have an established handicap. This is just the sort of situation confronted by organizers of corporate outings, charity days and beginner events.
The miclub system automates all processes so no manual calculation is required
CALLAWAY HANDICAP SCORING
The Callaway Method applies a onetime handicap that's actually based upon a player's score for the event.
Here's how it works:
As each player returns a score card for the round, an official scorer uses a "Callaway Table" to determine each golfer's net score for the round. Here is the Callaway Table used in the web site for a course with a par of 72.
The Callaway Method has these steps:
 Calculate "Adjusted Gross" by applying DoublePar stroke control to all holes
 Cross off the 16th, 17th and 18th holes. Some prefer to cross off just the 17th and 18th holes.
 Apply "Adjusted Gross" to the table to determine the Callaway Handicap entitlement (purple column)
 Identify the worst hole(s) on the score card to determine the Callaway Handicap
 Adjust the Callaway Handicap according to the bottom row of the chart
 Apply the adjusted Callaway Handicap to the "Gross" Score to obtain "Net"
Here are some additional rules:
 HalfStroke Entitlements are rounded up
 HalfHole Entitlement is applied to the smallest of the worst holes
 16th, 17th, 18th holes cannot be deducted Some prefer to exclude just the 17th and 18th holes.
 Tie for lowest net is won by player with lowest Gross
EXAMPLE 1
Howard turns in the score card shown below. His gross is 74, a very good score. It becomes the basis for all adjustments. The official scorer begins by applying "doublepar" stroke control to Howard's card. This means that the score for each hole is compared to double the par for that hole. If any score exceeds double par, the score is downwardadjusted to doublepar for that hole. In this case, none of Howard's scores exceeded doublepar. So Howard's "74" is also his "Adjusted Gross" score, not just his "Gross". The 16th, 17th and 18th holes are now eliminated from further consideration and are simply ignored according to the rules of Callaway scoring. 

Howard's Net score is a 72. And this is the figure that will be compared to those of the other competitors. 

The official scorer now looks at the Callaway Chart for "74" and finds it in the second row, second column of the table. The scorer then scans laterally to the right and from the purple column, we can see that Howard is entitled to a Callaway Handicap equivalent to 1/2 the score of his worst hole. Howard's worst hole was the 13th, where he scored a "6". By "worst hole", we mean "worst gross score regardless of par for the hole". So for the moment, Howard's Callaway Handicap is 1/2 of 6, which is "3". But there's one more step, and that is to apply the adjustment found on the bottom row of the Callaway Chart. Scanning down from the "74", we find the value of "minus 1". This figure must be added to the tentative Callaway Handicap. So, "3" plus a "1" equals "2". This is Howard's final Callaway Handicap, which is deducted from his Gross Score to form his Net Score for the competition. 74  2 = 72 

EXAMPLE 2  
Jeff turns in the score card shown left. His gross is 118. It becomes the basis for all adjustments. 

The official scorer begins by applying "doublepar" stroke control to Jeff's card. This means that the score for each hole is compared to double the par for that hole. If any score exceeds double par, the score is downwardadjusted to doublepar for that hole. 

In Jeff's case, the second hole required adjustment as did the 16th and 18th holes. He's only permitted to take a "10" on hole 2 and "8" on the 16th and 18th. Both the score for that hole and Jeff's Gross are adjusted downwards, giving him an "Adjusted Gross" score of 113 for the round. Now the 16th, 17th and 18th holes are eliminated from further consideration. In Jeff's case, we can see why this rule is used. It is quite common for players to "tank" towards the very end of the round, either due to tiring... Or simply due to "sandbagging" which is an overt attempt to try to drive up their handicap. 

The official scorer now looks at the Callaway Chart for "113" and finds it in the tenth row, third column of the table. The scorer then scans laterally to the right and from the purple column, we can see that Jeff is entitled to a Callaway Handicap equivalent to his 4 worst holes plus 1/2 the score of his fifthworst hole. 

Jeff's four worst holes are highlighted in yellow. He's also entitled to 1/2 of the fifth worst hole, also a seven. We've highlighted the first one in green. To calculate Jeff's Callaway Handicap, we add "10" + "9" + "8" + "7" to get "34". We also add 1/2 of the other "7", which gives a total of "37.5", which is rounded to "38". So for the moment, Jeff's Callaway Handicap is "38". But there's one more step, and that is to apply the adjustment found on the bottom row of the Callaway Chart. Scanning down from the "113", we find the value of "0", which means that his "38" Callaway Handicap remains at "38". This is Jeff's final Callaway Handicap, which is now deducted from his Gross Score (118) to form his Net Score for the competition. 118  38 = 80 Jeff's net score is an 80. And this is the figure that will be compared to those of the other competitors. 