With version 4.1 my 830 unit will consistently under- or overestimate gradients, often wildly so (displaying 19% during the climb of a 5% grade, or -7% while on reasonably level ground). At points during a ride the display's total ascent figure will seemingly 'freeze' only to instantaneously increase 600' or so after a few minutes. My end of ride cumulative ascent figures are 30+% more generous than they should be. Performed a reset to no avail. Have reverted unit to firmware version 3.5. Will see what happens...