Simple Powershell script to average

I'm looking to have a Powershell script written which will: 1) monitor a folder for new/modified files, 2)read the file, calculate the average of specified fields, and 3)write out a new text file in a subfolder containing the original fields and the calculated averages. The files which will be dropped off in the monitored folder will be in a text (.csv) file. Each file will have header information and rows of data. Each row will contain a fixed number of fields - a time stamp, record number, and a number of floating point data points. The script could read a configuration file which will identify the data points which need to be averaged (the number of fields could vary), calculate the averages, and write them to a new text file. Pls. see attached image for an illustration of what I'm looking for.