What is the maximum slope I can safely operate my lawn tractor on?

Do not operate the machine on a slope greater than 15 degrees, which is approximately a rise of 2.5 feet every 10 feet. Always mow up and down slopes, never across them, and use the Slope Gauge included in the manual to measure slopes before operating. If you cannot back up the slope or feel uneasy on it, do not mow it. (Page 8)