Abstract: A system for monitoring of a product quality variable of a moving web produced by associated equipment defines cross-direction (CD) data increments across a width of the web and machine direction (MD) data increments over a running length of the web, and takes CD/MD measurements of the selected variable in order to fill the corresponding CD/MD measurement data boxes and generate a time-dependent two-dimensional array mapping representing the moving web. In the preferred system, the CD data increments are divided across the width of the web, and the MD data increments are time-divided intervals of the time period of an element of the production equipment, so as to produce a time-synchronous array mapping which shows the impact of the periodicity of the machine element on the product quality variable.