+ For that purpose we need the "perfect response" function.

Input := 

g[x_] = If[x<100,0,1];
Input := 

Plot[g[x],{x,0,200}]
Output =

-Graphics-
Input := 

SumOfSquares = Sum[(data[[i]][[2]] - g[data[[i]][[1]] ])^2,
					{i,1,Length[data]}]
Output =

0.7024