A golf course is rated on its effective playing length and its playing difficulty under normal playing conditions. Consistency is the most important concept. The placement of tees and holes is the most obvious factor that can distort effective playing length. It may seem minor to move tees 10 yards back or up on each hole, but if you do so, the actual increase or decrease in the course and slope rating would be 0.8 and 2. The placement of tee markers on any given day should be representative of the effective playing length used when the course was rated. If you move the tees up 15 yards on one hole, make sure and add that 15 yards back to the course on one or more other holes.
Doglegs and forced lay-ups also have an impact on effective playing length. Any time you add an obstacle (large bunker or water) that forces a golfer to lay-up, the effective playing length increases. Conversely, you can reduce the effective playing length of a hole by removing a grouping of trees to allow golfers to go for a par-4 green in one shot. The last major component of effective playing length is roll. Softening or hardening fairways by using more or less water affects the amount of roll a player will get, thus increasing or decreasing the effective playing length of a golf course. As an example, if a course changes its water output so that the fairways change from firm to average, the course rating will go up by 0.5 and the slope rating by 1.
While not as strongly weighted as effective playing length, obstacle values are also used to determine a course and slope rating. If these obstacles are altered, your ratings may be slightly higher or lower than issued by your state golf association. Fairway widths on all par 4’s and par 5’s are recorded during a course rating. Thus, reducing your fairway width from 35 to 25 yards wide on all two and three shot holes will inflate your course and slope ratings. Raising or lowering mower blades to adjust your rough height has an impact on Recoverability and Rough, and can adjust the course/slope rating up to 0.7/5. OB and Extreme Rough can be misrepresented by changing the distance from out-of-bounds stakes to the center of your fairways. Strategically placed bunkers around landing zones or closely bordering greens will impact the Bunker obstacle values. The number of bunkers, their depth, and whether they must be carried to reach a target are all taken into consideration. Green Target, which measures the difficulty of hitting the green with the approach shot, could be reduced by watering your greens more than usual, thus changing then from average firmness to unusually soft. Lastly, contour and speed of greens have an impact on Green Surface; adjusting the Stimpmeter reading can cause the course/slope rating to fluctuate by 0.2/1.
As indicated before, maintaining the difficulty of your course from when it was last rated is instrumental in maintaining the integrity of course rating and handicapping. Making minor changes to your golf course and maintenance procedures can result in major inaccuracies to your course and slope ratings.