The 2-digit camber line is designated by a 2-digit number. The first denotes the maximum camber in percent of chord. The second digit denotes the chordwise position of the maximum camber, expressed in tenths of chord. A 24 camber line (or mean line) has a maximum camber of 0.02 chord located at 0.4c. The camber line is formed by two parabolic segments that match in value and slope (=0) at the maximum camber position. From these conditions, one may derive that the equation of each line is
y/ymax = 2*x/m -(x/m)2 if x ≤ m
y/ymax = (1-2*m + 2*m*x - x2) / (1-m)2 if x > m
where m is the position of the maximum camber as a fraction of chord and x is the position as a fraction of chord.
The NACA airfoil designation requires that m be an integer multiple of one-one-hundredth chord and ymax be an integer multiple of one-tenth chord, but the program will allow any fraction of chord for either quantity.
You may note that both NASA TM 4741 and Abbott and von Doenhoff use the parameters m and p to express the shape of the camber line, but the meanings of m and p are reversed. If you downloaded the PDF from NASA several years ago, the equation in NASA 4741 is incorrect. The copy on the NASA document server has now been corrected.