Bloodstain will be divide into two equal subsets (training set and validation set) according to a standard statistical approach called ome round cross-validation. The RGB value will be determined from the bloodstain in the training set and acalibration curve will be constructed. These curve will then be used to estimate the age of bloodstain in the validation set. The range of the estimated age of all bloodstain in the validation set measured at a single time point indicates the error margin of the estimation.