Scroll steadily in one intended direction inside the capture area. GearCheck Lab records browser wheel events, counts opposite-direction events and compares delta values so intermittent reverse jumps can be reproduced without assuming every browser event equals one physical wheel notch.
Browsers expose wheel events with delta values. A physical detent can result in one or several browser events depending on the mouse, driver, operating system, smooth-scrolling software and browser.
During a deliberate one-direction run, an event with the opposite deltaY sign is useful evidence of the symptom commonly described as scroll-wheel jumping backward. Repeated opposite events are more meaningful than one isolated event.
Dust, encoder wear, vendor software, touchpad emulation, drivers or browser/OS smoothing can all contribute.
The median absolute delta gives context for the event scale produced by the current environment. Very different delta sizes are not automatically bad: high-resolution/free-spin wheels and different deltaMode values can legitimately vary.
A webpage cannot know that a physical notch occurred if the system sends no event at all. If you physically feel a notch but see no movement/event, repeat slowly and note the symptom manually. The page is strongest at detecting signals it actually receives, especially reversed ones.
Touchpads and high-resolution wheels can generate many small deltas and inertia events. This diagnostic is most useful for a conventional mouse wheel when you can keep the physical direction steady and stop cleanly.
No. Repeat the run and compare another environment. Several opposite events during deliberate one-direction wheel movement are stronger evidence than one.
Operating-system settings, browser scaling, smooth scrolling, high-resolution wheels and delta mode can change the reported amount.
Not directly. If no browser event arrives, the page has nothing to timestamp. Use the live counter alongside what you physically feel.