Scroll Test

A scroll test counts every step your mouse wheel sends and flags any step that goes the wrong way. Put the cursor in the box above and roll the wheel slowly, then fast, in both directions: if Up and Down climb with every step and Reverse jumps stays at 0, the wheel is working.

How to use the scroll test

1. Move the cursor into the box that says Scroll here. The page itself will not scroll while the cursor is inside it.
2. Roll the wheel down slowly, one notch at a time, for ten or more notches. Then do the same going up.
3. Repeat both directions with fast, long spins. Most wheel faults only show up at one speed.
4. If your mouse has a tilt wheel, push it left and right.
5. Read the five counters under the box. Press Reset to start over.

As you scroll, each step draws a small bar inside the box. Bars for upward steps sit higher and bars for downward steps sit lower, so a clean scroll looks like a level row. A step flagged as a reverse jump is drawn in a different colour and sits on the opposite level, which makes it easy to spot. The row shows the latest 60 steps.

The message in the box sums up the run. Every step went the right way means no fault has been caught. A message such as 2 steps jumped backwards means the wheel reported the wrong direction twice.

What do the scroll test numbers mean?

Counter	What it counts	Healthy result
Up	Scroll steps reported upward	Rises by one for each notch on a standard notched wheel
Down	Scroll steps reported downward	Rises by one for each notch on a standard notched wheel
Reverse jumps	Steps that went against the direction you were scrolling	0
Tilt / horizontal	Left and right scroll steps	Rises only when you tilt the wheel or scroll sideways
Distance	Total vertical scroll distance, in px, as reported by the browser	Grows steadily in even amounts

Two notes on reading these. First, the counters show scroll events, not physical notches. A classic notched wheel normally sends one event per notch, but smooth-scrolling wheels and free-spin modes can send many small events per turn.

Second, the distance per step is not a property of the mouse alone. It depends on the scroll speed set in your operating system and on the browser, so the same wheel gives different px totals on different computers. Use Distance to compare runs on one machine, not as an absolute measurement.

How the reverse jump detection works

A reverse jump is the fault people describe as "I scroll down and the page twitches up". The test flags a step as a reverse jump when all three conditions are true:

• You had already scrolled at least two steps in a row in one direction.
• The next step arrived in the opposite direction.
• It arrived within 150 ms of the step before it.

That timing is what separates a fault from a change of mind. If you stop and deliberately scroll back, the pause is longer than 150 ms and nothing is flagged. A wheel in good condition does not produce an opposite step in the middle of a continuous roll.

One side effect: if you flick the wheel back and forth as fast as you can, you can trigger a flag yourself. To test fairly, scroll in one direction at a time and pause briefly before reversing.

Why does a mouse wheel jump or skip?

Behind the wheel is an encoder. It turns rotation into electrical pulses, and the order of those pulses tells the mouse which direction you turned. Most mice use a mechanical encoder with small metal contacts; some use an optical one that reads light through a slotted wheel.

Both types fail in a similar way. Dust, hair and skin debris get into the gap around the wheel and into the encoder. In mechanical encoders the contacts also wear and oxidise. The pulses then arrive incomplete or out of order, and the mouse reads one step as going the other way, or misses it.

Symptom	Likely cause	First thing to try
Page jumps the opposite way during a scroll	Dirty or worn encoder	Compressed air into the wheel gap while turning the wheel
Steps are skipped at slow speed	Worn encoder contacts or weak notch mechanism	Clean first; replace the encoder if it persists
Works slowly but fails on fast spins	Encoder cannot keep up because of dirt or wear	Clean, then retest at both speeds
Wheel feels gritty or squeaks	Debris on the wheel axle	Clean the axle and wheel gap
Scroll distance is uneven but the direction is right	Software smoothing or acceleration	Check OS scroll settings and the mouse software
Scrolling stalls on a wireless mouse	Low battery or a weak connection	Charge it and move the receiver closer

How to fix a scroll wheel that fails the test

Work from the least invasive step to the most.

1. Blow out the wheel. Unplug the mouse or turn it off. Aim short bursts of compressed air into the gap on both sides of the wheel while you turn it. Retest.
2. Rule out software. Try the mouse on another computer, or close the manufacturer's software and retest. If reverse jumps disappear, a driver or smoothing feature is involved.
3. Check power and connection on a wireless mouse. Charge or replace the batteries and move the receiver away from other USB devices.
4. Update the firmware if the manufacturer offers an update for your model.
5. Check the warranty before opening anything. A wheel that scrolls the wrong way is a hardware defect, and opening the mouse may affect your claim.
6. Clean or replace the encoder. Out of warranty, you can open the mouse and clean the encoder with electrical contact cleaner. If the fault returns, the encoder itself is worn. Replacing it requires soldering and a part that matches your model.

Cleaning often helps for a while. If reverse jumps come back within days or weeks, treat the encoder as worn rather than dirty.

Testing a tilt wheel and horizontal scroll

The Tilt / horizontal counter shows left and right steps side by side. Tilt the wheel each way and check that the matching number rises. Mice with a second, sideways wheel report here too.

If your mouse has no tilt function, this counter normally stays at zero. In many browsers, holding Shift while you roll the wheel is reported as horizontal scrolling, so a non-zero number is not a fault if Shift was held.

Limits of a browser scroll wheel test

• It reads what the browser receives. Drivers and operating system settings can reshape scroll input before the page sees it. Retesting on a second computer separates the mouse from the software.
• Touchpads and touch-surface mice behave differently. They send a stream of small events and keep scrolling with inertia, so step counts are not comparable to a notched wheel.
• The wheel click is not covered. The middle button is a separate switch under the wheel.
• A clean run is a snapshot. Intermittent encoder faults may need several runs at different speeds to appear.

Related tests

The wheel is one part of the mouse. The full mouse test checks the middle click along with every other button in one panel. If your buttons are also misbehaving, the double click test catches a switch that registers one press as two.

For sensor and connection checks, the DPI test measures how far the cursor really travels per inch of movement, and the polling rate test shows how often your mouse reports to the computer.