A nice bonus page explains how to use #32, #64, or #117B rubber bands for light/medium/heavy power, plus warnings about eye protection. Safety-conscious makers will appreciate this.
Look for a "Scale Check" on the PDF. A reputable designer will include a 1-inch or 10-centimeter reference square on the page. You can measure this with a ruler after printing to ensure the template hasn't been shrunk or expanded by your printer settings. Rubber Band Gun Template Pdf