109 addition fact cards, grouped by sum from 1 through 19 (e.g. sum 16: 0+16,
1+15, ... 8+8). Front: the expression. Back: the sum. Printing produces
28 pages — a front page followed by its matching back page,
8 cards each. Print double-sided, Landscape, with Margins: None and "flip on long edge" — with default margins, browsers
auto-scale each page to fit the printable area, and that scale factor drifts between the
front and back cards, throwing off the cut alignment.