53 terms you’ll run into when a keyboard, mouse, monitor or headset misbehaves. Each one says what it means in practice and links to the test that checks it.
Also called ANSI · ISO · keyboard layout
ANSI and ISO are the two common physical keyboard shapes. ANSI has a wide one-row Enter key and a long left Shift while ISO has a tall Enter key and an extra key beside a shorter left Shift.
Physical shape and software layout are separate. A UK ISO keyboard set to a US layout types the wrong symbols on several keys without anything being faulty.
Also called debounce time
Debounce is the short window after a press during which a keyboard or mouse ignores extra signals from the same switch. Metal contacts bounce for a few milliseconds when they meet and debounce stops that from counting as several presses.
As a switch wears its bounce gets longer. Once it outlasts the debounce window the device starts sending double presses, which is where chatter comes from.
Also called keyboard ghosting
Ghosting is when pressing a certain combination of keys makes a keyboard report an extra key you never pressed. It comes from the way cheaper keyboards wire their keys in a shared grid.
True ghosting is rare on modern keyboards because they block the phantom key instead. What most people call ghosting today is key blocking.
Also called key jamming · anti-ghosting
Key blocking is when a keyboard ignores a key you pressed because registering it could produce a ghost key. The key works on its own but drops out when held with certain other keys.
Hold the combination you use in a game on the keyboard test. If one key never lights up while the others are held it is being blocked, not broken.
Also called double typing · switch chatter
Key chatter is one key press registering as two or more characters. It usually means a mechanical switch is dirty or worn and its contacts bounce when they close.
Chatter is different from key repeat, which is the operating system repeating a key you are still holding. Cleaning the switch fixes some cases and replacing it fixes the rest.
Also called KeyboardEvent.code · scan code
A key code identifies the physical position of a key, separate from the character it types. The same key reports the same code on a US layout and a French layout even though it types a different letter.
The keyboard test lights keys by code. If the right key lights up but the wrong letter appears in documents the keyboard is fine and the operating system layout is wrong.
Also called typematic rate · repeat delay
Key repeat is the operating system typing a character over and over while you hold its key down. The delay before repeating starts and the speed of repeating are system settings, not properties of the keyboard.
If characters repeat when you tap a key briefly check the repeat delay setting before you blame the hardware.
Also called key switch
A mechanical keyboard switch is an individual spring and contact assembly under each key. Each switch can fail on its own, which is why one dead key on a mechanical keyboard is often repairable.
Also called NKRO · 6KRO · key rollover
Key rollover is the number of keys a keyboard can register at the same time. A keyboard with N-key rollover registers every key you hold at once while a 6KRO keyboard stops at six.
The keyboard test reports your peak rollover: the most keys it saw held down together. USB keyboards running in boot mode are limited to six regular keys plus modifiers, so a lower number than the box promises can be a mode setting rather than a fault.
Also called CPS · click speed
Clicks per second is how many times you click in one second, averaged over a short run. It measures your finger speed rather than the health of the mouse.
The mouse test averages CPS over five seconds. Very fast clicking techniques can land two clicks close enough together to look like chatter, which is why the test says so when it flags one.
Also called CPI · dots per inch · counts per inch · mouse sensitivity
DPI (more accurately CPI) is how many position counts a mouse sensor reports for each inch you move it. Higher DPI moves the cursor further for the same hand movement.
A web page only sees cursor movement after the operating system has applied its own speed setting, so no browser test can read the true DPI of a mouse.
Also called micro switch · Omron switch
A mechanical mouse switch closes two metal contacts when you click. They are rated in millions of clicks but wear and oxidation make them bounce long before that rating in many cases.
Also called enhance pointer precision · pointer acceleration
Mouse acceleration moves the cursor further when you move the mouse quickly than when you move it the same distance slowly. Windows calls it Enhance pointer precision and turns it on by default.
Also called double click chatter · double clicking issue
Switch chatter is when a single mouse click registers as two. The metal contacts inside a worn mechanical switch bounce as they close and the mouse reports the bounce as a second click.
The mouse test flags any two clicks on the same button less than 50ms apart. That is faster than a person can double click on purpose, so a flag there points at the switch rather than your finger.
Also called light switch · optical mouse switch
An optical switch detects a press when the button interrupts a beam of light instead of closing metal contacts. With no contacts to bounce it can’t develop the classic double click chatter.
An optical mouse that double clicks is pointing at firmware or settings rather than a worn switch.
Also called report rate · 1000Hz
Polling rate is how often a mouse or keyboard sends its state to the computer, measured in Hz. At 1000Hz the device reports every millisecond and at 125Hz every eight milliseconds.
A very high polling rate on a busy USB port can cause stutter. Dropping it one step is a quick test when the cursor hitches.
Also called scroll encoder
The encoder is the part that turns scroll wheel rotation into scroll steps. When a mechanical encoder gets dirty or worn the page jumps or scrolls briefly in the wrong direction.
Also called light bleed · clouding
Backlight bleed is light leaking around the edges of an LCD panel. It shows as bright patches near the corners on a black screen in a dark room.
Bleed stays in the same place when you move your head. That separates it from IPS glow, which shifts with viewing angle.
Also called OLED burn-in · screen burn
Burn-in is a permanent faint image of something that stayed on an OLED screen for a long time, such as a taskbar or a game HUD. It happens because pixels that are lit more often wear faster than the ones around them.
It is easiest to see on a full screen mid gray or on solid red, green and blue. A shape that fades within minutes is image retention instead.
A dead pixel stays black on every color because it no longer lights at all. It shows up most clearly against a white or bright full screen color.
Dead pixels are usually permanent. Record where they are before you contact the seller since most return policies count them.
Also called pixel warranty · zero bright dot
A dead pixel policy is the manufacturer’s rule for how many faulty pixels a screen must have before it qualifies for repair or replacement. Many brands require several defects or a bright dot in the center of the screen.
The number and type of pixels matter, so photograph each one against the color that shows it best before you file a claim.
Also called frame interval · frametime
Frame time is the gap between one frame and the next, measured in milliseconds. At 60Hz each frame lasts about 16.7ms and at 144Hz about 6.9ms.
The refresh rate test samples frame intervals for two seconds and reports how much they vary as well as their average.
Also called temporary burn-in · ghosting on OLED
Image retention is a temporary trace of recently static content that fades on its own. It looks like burn-in but disappears after a few minutes or after the screen runs its standby compensation cycle.
IPS glow is a hazy silver or warm sheen visible on dark content on IPS panels, especially from an angle. It is a property of the panel type rather than a defect.
Also called LFC · frame doubling
Low framerate compensation shows each frame two or more times when a game drops below the bottom of a monitor’s variable refresh range. It keeps the refresh rate inside the range so variable refresh keeps working.
A frame rate that keeps crossing that threshold switches it on and off, which is one cause of flicker on variable refresh monitors.
Also called screen uniformity · dirty screen effect · DSE
Uniformity is how evenly a screen shows a single flat color from edge to edge. Poor uniformity shows as darker corners, tinted areas or faint banding on a plain gray.
Also called PWM flicker · pulse width modulation
PWM dimming lowers a screen’s brightness by switching the light on and off very rapidly instead of reducing it steadily. Some people see it as flicker or get eye strain from it, mostly at low brightness settings.
Also called Hz · hertz · 144Hz
Refresh rate is how many times per second a monitor draws a new image, measured in hertz. A 144Hz monitor can show up to 144 distinct frames every second.
The refresh rate test measures the rate your browser is actually receiving, which catches a high refresh monitor left at 60Hz by a cable or a Windows setting.
Tearing is a horizontal split across the screen where the top and bottom show different frames. It happens when a new frame arrives while the monitor is part way through drawing the previous one.
Also called hot pixel · bright dot
A stuck pixel has one or more subpixels stuck on, so it shows a fixed red, green, blue or white dot on every background. It is most visible on a black screen.
Unlike dead pixels, stuck pixels sometimes recover with pressure or a rapidly flashing color, though there is no guarantee.
Each pixel on an LCD or OLED screen is made of red, green and blue subpixels that mix to form its color. A fault in a single subpixel produces a colored dot rather than a black one.
Also called vertical sync
V-Sync makes a game or app wait for the monitor to finish a refresh before it shows the next frame. It removes tearing but adds input delay and can cause stutter when frames arrive late.
Also called VRR · G-Sync · FreeSync · adaptive sync
Variable refresh rate lets a monitor wait for each new frame instead of refreshing on a fixed clock. G-Sync and FreeSync are the common brand names and both prevent tearing without the delay of V-Sync.
When frame intervals vary widely the refresh rate test reports that variable refresh is probably active. In that case the number it shows is an average rather than the panel maximum.
Also called analogue axis · axis value
An analog axis reports a range of values rather than on and off. Each stick has a horizontal and a vertical axis. Browsers report each one from -1 to 1 with 0 at the center.
Analog triggers work the same way on a scale of 0 to 1. A trigger that never reaches 1 at full press is out of calibration or physically blocked.
Also called dead zone
A deadzone is the small area around a stick’s center that a game treats as no input. It hides the slight resting offset every stick has but it also swallows very small deliberate movements.
Also called Hall effect joystick · magnetic stick
A Hall effect stick measures position with a magnet and a sensor instead of a sliding contact. With no contact to wear it is far less prone to the drift that affects potentiometer sticks.
Also called pot stick · ALPS stick
Most controller sticks measure position with potentiometers: a contact that slides along a resistive track. Wear and dust on the track are the most common cause of stick drift.
Steam Input is Steam’s controller layer. It reads PlayStation, Switch and generic controllers and presents them to games as a standard controller or as keyboard and mouse input.
It only applies to games launched through Steam. When a game also reads the controller directly every press can arrive twice.
Also called joystick drift · analogue drift · Joy-Con drift
Stick drift is when an analog stick reports movement while nobody is touching it. Games read it as input, so your character or camera moves on its own.
The controller test reads each axis at rest on the browser scale of -1 to 1. Readings up to 0.05 are normal tolerance and anything above 0.10 usually beats the deadzone in games.
Also called XInput · DirectInput
XInput and DirectInput are two Windows interfaces games use to read controllers. Many modern PC games only support XInput, which is why a controller that works everywhere else can be ignored by a game.
A browser reads controllers through its own interface, so passing the controller test proves the hardware works but not that a particular game will accept it.
Also called audio delay · Bluetooth latency · lip sync
Audio latency is the delay between a sound being produced and you hearing it. Bluetooth adds noticeably more than a wired connection because audio has to be compressed and buffered before it is sent.
Also called HFP · headset mode
The hands-free profile is the Bluetooth mode a headset switches to when its microphone is in use. It carries sound both ways at a much lower quality, which is why music can turn thin the moment a call starts.
Also called audio clipping · peaking
Clipping happens when a signal is louder than the maximum a device can record or play, so the tops of the waveform are cut off. It sounds harsh and distorted and can’t be repaired after recording.
Also called frequency range · 20Hz to 20kHz
Frequency response is the range of pitches a speaker or headphone can reproduce and how evenly it plays them. Human hearing covers roughly 20Hz to 20kHz and small speakers lose the low end first.
The speaker test sweeps from 20Hz to 20kHz. Buzzing or rattling at one point in the sweep can mean a loose part rather than a failing driver.
Also called echo cancellation · automatic gain control · AGC
Noise suppression filters background sound out of a microphone signal. Browsers and meeting apps usually apply it together with echo cancellation and automatic gain control, which all change how your voice sounds.
The microphone test turns all three off so you hear what the microphone itself captures. A voice that sounds fine there but muffled in a call points at the app’s processing.
Also called kHz · 48kHz · 44.1kHz
Sample rate is how many times per second audio is measured when it is recorded, given in kHz. Most microphones run at 44.1kHz or 48kHz, which is plenty for speech.
The microphone test shows the sample rate your browser negotiated with the device.
Also called left and right channels · balance
Stereo audio has two channels, left and right, each sent to its own speaker or earcup. Sound from only one side usually means a balance setting, a mono setting or a loose connector.
Also called camera in use · device in use
On Windows a webcam can usually be used by only one application at a time. A second app trying to open it gets an error or a black picture until the first app lets go.
Also called fps · frames per second
Frame rate is how many images a camera sends each second. Webcams commonly run at 30fps and many drop lower in dim light because each frame needs a longer exposure.
Also called 1080p · 720p
Resolution is the number of pixels in each frame a camera sends, such as 1920 by 1080 for 1080p. A camera often runs below its maximum if an app asks for less or a USB port can’t carry the full stream.
The webcam test asks for 1080p and reports what the camera actually delivers.
Also called getUserMedia · site permissions
Browsers only let a page use your camera or microphone after you allow it. The operating system can also block access for every browser at once. A blocked permission looks exactly like a broken device.
The webcam and microphone tests process everything on your device. Nothing is uploaded.
Also called standard mapping
The Gamepad API is how a browser reads controllers. It maps common controllers to a standard button layout, which lets one test page work with Xbox, PlayStation and many third party pads.
Browsers only expose a controller after you press a button on it. That is a privacy rule, not a detection fault.
Also called human interface device
HID is the standard most keyboards, mice and controllers use to talk to a computer over USB or Bluetooth. Because it is a standard these devices usually work without a special driver.
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This glossary covers what our troubleshooting guides and tests actually deal with. If a word on one of our pages isn’t explained here, tell us through the contact page and we’ll add it.
