Hi professor Wise, The sample1.xslx could not be accessed on my device, and got a warn "The specified resource was not found or you do not have permission to access it." I am not sure is there any problem with this file. Also, as the Ass2 says: "contents of the input files may change", I am concerning that should we assume that all the value in the input file is under the reasonable format, for example, there would not have an invalid value like "2@20" in years so that we need to handle this error. Best regards. Zhiyang