You will get three numbers for each bin in the output, total(value), which is sum of all entries in the scorer, total(val^2), which is sum of all entries squared and entry, which is number of entries in the scorer. You can calculate the variance as total(val^2)/(number of runs)-(total(value)/(number of runs))^2, and from that the standard error of the mean as sqrt(variance/(number of runs)) and relative error sqrt(variance/(number of runs))/(total(value)/(number of runs)).