The NewPage command does not use any particular measurement system. It divides your page into arbitrary units you decide, without regard for page size or shape. In other words, the command tells Sesame to divide the page into a grid. The number of horizontal cells and vertical cells in that grid are the parameters passed to NewPage.

So, NewPage(800, 1600)

will divide the page into 800 units across and 1600 units down, no matter how big you page is. The purpose of the parameters is to give the programmer control of how fine a resolution they want to work. The larger the parameters, the finer the control.