Scratch Player Difficulty (SPD) measures the difficulty of a disc golf course for an expert player (Gold, 1000 rating). The more trees, terrain, obstacles and out of bounds areas there are per length of the course, the higher the difficulty and the higher the SPD. SPD recognizes that a course with the same density of obstacles that is longer is proportionally harder than a shorter course with the same density of obstacles.
SPD combines the Challenge Factor (CF) with a factor for course length.
CF = [(SSA-30)/ Actual Course Length] * 20,000
Length Factor (LF) = Actual Length (standardized to 18 holes)/100.
*Dividing by 100 converts the length to a number from 10-100. e.g.- a length of 5400 ft = 54.
SPD = [CF + LF - 73]*0.1
*The constant 73 puts the SPD on a 0-100 scale. It is derived from empirical data collected from ~150 course layouts.
*The factor of 0.1 makes it on a 0-10 scale.