The regression minimizes the residual sum of squares (RSS). In this game, the player chooses slope and y-intercept
of a line so as to approximate the regression line. The moveable line is set initially as a horizontal line with height equal to
the mean of the y-coordinates of the scatterplot, so initially the residual sum of squares equals the total sum of squares (TSS).
The player's score is the sum of the number of turns taken and the difference between the current RSS
and the regression line's RSS (as a percentage of TSS-RSS for regression line). The aim is to lower one's score.