Mouse Scroll Test for a Scroll Wheel That Skips

Press Start, roll the wheel slowly over the box and see each tick as an arrow, with wrong-way ticks marked.

Press Start, put the pointer here and roll slowly.

No ticks yet.

0 ticks

While a run is on, the page does not scroll with the pointer in this box. A run ends after two still seconds, on Stop or on Esc.

Tick size: not read yetOpposite: 0Middle button: 0 presses, 0 releases

More options

Your last five runs

  1. No run yet.

Nothing from this test is stored unless you tick the box. Kept runs are numbers only and never leave this browser.

How this check works

Slow roll down, 30 notches

Roll towards you one notch at a time, about two a second. Each tick lands in the strip as an arrow. Thirty arrows should all point the same way. Slow and steady matters: a wheel that misreads often does it at low speed, when each contact of a mechanical encoder makes and breaks lazily.

Every wheel event is one tick. The page counts ticks and their direction, and it never judges the wheel.

  • Every wheel event the browser sends is one tick, with a direction and a size in pixels, lines or pages.
  • A tick counts as opposite when it goes against most of its own run, so natural scrolling changes nothing.
  • The middle button is followed from press to release, and any tick that arrives while it is down is counted.

Result

No ticks yet.

What this means

Ticks
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Opposite
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Tick sized in
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Middle presses
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Next step Wheel reads clean? Race it over 10 secondsSame mouse, next check: its report rate

All 21 checks

Wheel checks, one at a time 9

  • Slow roll down, 30 notches Roll towards you one notch at a time, about two a second. Each tick lands in the strip as an arrow. Thirty arrows should all point the same way. Slow and steady matters: a wheel that misreads often does it at low speed, when each contact of a mechanical encoder makes and breaks lazily.
  • Slow roll up, 30 notches The same check away from you. Rolling the other way fires the encoder's two signals in the opposite order, so a wheel can be clean in one direction and misread in the other. Run both before you decide anything.
  • Count 20 notches aloud Feel each notch and count it yourself, then compare with the page. Twenty felt and 20 shown is a match. Seventeen shown means three steps turned without a signal. Forty shown means your wheel sends two ticks a notch, which some do by design.
Show all 21 checks (18 more)

Wheel checks, one at a time, continued

  • Fast flick, then let it stop Spin the wheel hard once and take your finger off. The strip marks any arrow that points against the rest. Judge the middle of the spin: a single opposite arrow as the wheel comes to rest can be the wheel dropping back into its notch.
  • Free-spin wheel, one long spin For wheels that can be switched to spin freely. One spin sends far more ticks than a notched roll, which makes this the longest direction check on the page. There are no notches to count in this mode, so only the direction of each tick is checked.
  • Hands off for 10 seconds Let go of the mouse and watch. Any tick that arrives is one you did not send. A wheel left balanced between two notches is the usual source, so nudge it into a notch and run the ten seconds again before reading anything into it.
  • Middle click, 10 presses Press the wheel straight down ten times. The page counts a press and a release for each, and shows any tick that slips in while the button is down. Ten presses, ten releases and no ticks is a clean run.
  • Middle click and hold, five seconds Drawing and 3D programs pan or orbit while the wheel is held down, so the button has to stay down. Hold for five seconds. A release and a new press that you did not make will show as a break in the bar.
  • Tilt or side wheel, 10 ticks each way For a wheel that tilts, or a second wheel under the thumb. Sideways ticks show as left and right arrows. If none arrive, the mouse's own software may have given the tilt another job, such as back and forward.

How the browser sizes a tick 3

  • Tick sized in pixels (mode 0) The browser reports each tick as a distance in pixels. The size is set by the system and the browser, not by the wheel, so two computers can give one mouse different sizes. A wheel check reads direction and count and ignores size.
  • Tick sized in lines (mode 1) The browser reports each tick as a number of lines of text and leaves the page to decide how tall a line is. On Windows the wheel setting is three lines a notch by default. Same wheel, different unit. Nothing about the hardware has changed.
  • Tick sized in pages (mode 2) One tick means one whole screen. Windows has a wheel setting for one screen at a time in place of a number of lines, and a browser may pass that on in this unit. If every notch jumps a full page everywhere, look at that setting before you look at the mouse.

Wheel readings that need a second look 9

  • A tick the wrong way in a steady roll An encoder sends two signals a quarter of a cycle apart, and direction is read from which one leads. In a mechanical encoder the signals come from sliding contacts, and if one bounces or misses, the order looks swapped and one step is reported backwards. In a mechanical encoder that can point to dirt or wear. Blow out the wheel slot, then try another port and another computer.
  • Fewer ticks than notches The wheel turned and no signal came. First rule out the page: the pointer must stay over the box, and the box must be the active tab. If the shortfall repeats with the pointer in place, the wheel is missing steps.
  • Two or more ticks for every notch Steady doubling is a design, not a fault. One widely used system counts a notch as 120 units so that finer wheels can send more, smaller messages. What deserves a second look is doubling that comes and goes: 1, 1, 2, 1, 1, 2.
  • One opposite tick as the wheel stops At the end of a flick a wheel can stop between notches and drop back into the nearer one, which is a real movement in the other direction. It matters in games that bind a weapon to each direction. It does not by itself point to a worn part.
  • Ticks with nobody touching the wheel Seat the wheel in a notch and repeat the hands-off check. On a laptop, keep your palm off the trackpad, because a trackpad sends the same kind of event and the page cannot tell them apart. Ticks that persist came from the wheel.
  • A wheel tick during a middle click Pressing the wheel turned it a fraction. In a browser that means a link opens in a new tab and the page jumps. Press straight down through the centre of the wheel. If ticks still slip in, the press is heavier than the notch is firm.
  • Middle click missing or never released A press with no release often means the pointer left the box before you let go. No press at all often means mouse software has given the button another job. Check its settings, then try a second browser.
  • Hundreds of tiny ticks from one stroke That is a trackpad, a touch-surface mouse or a wheel with no notches. They report many small movements in pixels and often add a glide after you let go. The direction check still works. The notch count does not apply.
  • No ticks at all on a phone or tablet A finger drag is not a wheel event, and at least one major phone browser is recorded as not sending wheel events to pages at all. This page needs a mouse on a computer. For the screen itself, use the touchscreen test.

How this list was compiled: Table written for this page. Every check is a fault check and none is scored for speed: the speed rounds live on the scroll test page. That a scroll wheel is built round a rotary encoder, that the wheel is often, but not always, built with detents so that it turns in discrete steps, that pressing the wheel gives a third button, that some wheels tilt to scroll sideways and that natural scrolling inverts the direction follow https://en.wikipedia.org/wiki/Scroll_wheel. That an encoder sends two signals a quarter of a cycle apart, that direction is read from which signal leads, and that the sliding contacts of a mechanical encoder bounce and must be filtered to avoid count errors follow https://en.wikipedia.org/wiki/Incremental_encoder (both checked 2026-09-19). Neither article says which kind of encoder a given mouse uses, so the table speaks of contacts only where it names a mechanical encoder. That some wheels can be switched to spin freely, and that a free spin sends far more ticks than a notched roll, is this page's own observation; no figure is given because no source for one was found. The three units a browser may use for the size of a wheel event (pixels 0, lines 1, pages 2) are from https://developer.mozilla.org/en-US/docs/Web/API/WheelEvent/deltaMode. The defaults of a middle press (usually autoscroll on Windows and clipboard paste on Linux) and how a page holds them back are from https://developer.mozilla.org/en-US/docs/Web/API/Element/auxclick_event. Browser support was read from api/Element.json in https://github.com/mdn/browser-compat-data, keys api.Element.auxclick_event (Chrome 55, Firefox 53, Safari 18.2) and api.Element.wheel_event (Chrome 31, Firefox 17, desktop Safari 7, not supported in Safari on iOS), all checked 2026-09-19. That one notch is 120 units on Windows, and that the figure was chosen so that finer wheels with no notches can send more messages with a smaller value in each, is from https://learn.microsoft.com/en-us/windows/win32/inputdev/wm-mousewheel (checked 2026-09-19). That the Windows wheel setting is 3 lines a notch by default, and that it can be set instead to scroll one screen at a time (the value WHEEL_PAGESCROLL), is from https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-systemparametersinfoa, entries SPI_GETWHEELSCROLLLINES and SPI_SETWHEELSCROLLLINES (page dated 2024-03-27, checked 2026-09-19); both figures are worded as holding on Windows. MDN's deltaMode page lists the three units and says nothing about when a browser uses each, so the table says a browser may pass the one-screen setting on as the pages unit and does not say that it does. That the pixel size of a tick is set by the system and the browser and not by the wheel is this page's reasoning from the fact that the browser chooses the unit. What a reading suggests is this page's reasoning from those mechanisms and is worded as a suggestion, never as a verdict on a mouse. Licence: own work

How it works

Roll the wheel and this mouse scroll test draws each tick as an arrow, marking any that point against the rest. It gives no speed score: it sets ticks against notches and checks the middle click.

Read the full guide

Roll slowly and watch the arrows

Start with Slow roll down, 30 notches, already chosen under Check to run. The run ends after 30 ticks or two still seconds. Thirty arrows should point one way. If some do not, the result reads: 2 of 31 ticks reported the opposite direction. Then pick Slow roll up, 30 notches and press Start. A wheel can misread one way only.

Why a wheel scrolls the wrong way

Inside the wheel a rotary encoder sends two signals a quarter of a cycle apart, and direction is read from which one leads. A mechanical encoder makes them with sliding contacts, which bounce. When dirt or wear makes one bounce too long or miss, the order looks swapped and one step goes backwards.

  • Run Count 20 notches aloud: fewer ticks than notches means missed steps. Type your own count in Notches you counted.
  • Judge the middle of a flick. One opposite arrow as the wheel stops can be it settling into a notch.
  • Keep your palm off a laptop's trackpad: it sends the scroll wheel tester the same events as a wheel.

Questions and answers

Why does my mouse scroll up when I scroll down?

One cause is the wheel's encoder misreading a step, so one tick in a steady roll comes out reversed. If every tick goes the wrong way, look for a natural scrolling setting. Blow out the wheel slot, then run the scroll wheel test again.

How do I test the middle mouse button?

Pick Middle click, 10 presses and press the wheel straight down inside the box. The page counts each press and release, and any tick that slips in meanwhile. Middle click and hold, five seconds checks that the button stays down for panning.

Does the mouse wheel test work on a phone or a trackpad?

A trackpad works, but it sends a stream of movements with no notches, so only direction is checked. A phone does not: a finger drag is not a wheel event, and Safari on iPhone and iPad is recorded as sending none. Try the touchscreen test.

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