Glossary
The terms that appear across this site, defined in one sentence each. Where a term is commonly misused, the definition says how.
| Term | Definition |
|---|---|
| Buttock to popliteal length | The distance from the back of the buttocks to the back of the knee. It sets how deep a seat pan can be before the front edge presses into the calf, which is the commonest chair fit failure. |
| Popliteal height | The height from the floor to the underside of the thigh at the back of the knee, sitting with feet flat. It sets seat height. |
| Seat pan | The part of the chair you sit on. A sliding or adjustable pan changes its usable depth, which is the single most useful adjustment for anyone whose leg length is not average for their height. |
| Waterfall edge | A rounded front edge on a seat pan, which reduces pressure on the underside of the thigh. It softens a slightly deep seat and cannot rescue a badly deep one. |
| Lumbar apex | The point of maximum forward projection of a chair back support. It should meet the inward curve of your lower back, which is why height adjustment matters more than depth adjustment. |
| Gas cylinder | The pneumatic column that raises and lowers a chair seat. Largely a commodity part, and the usual culprit when a chair sinks under load. Replacing one is cheap. |
| BIFMA X5.1 | The test standard for general purpose office chairs, covering static load, drop, durability and stability testing. |
| BIFMA X5.11 | The separate test standard for large occupant office chairs. A chair certified to X5.1 has not been tested to X5.11. |
| ANSI/HFES 100 | The consensus standard for computer workstation fit. It specifies adjustment ranges for populations rather than single correct dimensions for individuals. |
| Duty cycle | How much of a period a standing desk motor may run. Commonly stated as 10 percent, or 2 minutes on and 18 minutes off. Ample for normal use, and not intended for repeated cycling. |
| Lift capacity | The load a height adjustable frame raises above itself. Normally quoted EXCLUDING the tabletop, which can weigh 33 to 95 lb, so the usable figure is lower than the headline. |
| Dual motor | A frame with one motor per leg. Lifts faster than a single motor design, around 1.5 in/s against 1.0, and stays level under an uneven load such as a tower on one side. |
| VESA pattern | The standard hole spacing on the back of a monitor for mounting. 75 x 75 mm and 100 x 100 mm are the usual desktop sizes, with 200 x 100 mm on larger panels. |
| Gas spring arm | A monitor arm counterbalanced by a gas cylinder, rated for a RANGE of weights. A panel below the range floats up; a panel at the top of the range sags as the spring ages. |
| Pixel density (ppi) | Pixels per inch on a panel. It sets the distance at which the pixel grid stops being resolvable, which is why a higher resolution panel can be viewed from closer, not further. |
| Pixels per degree | How many pixels fall within one degree of your field of view. Around 60 is the usual comfort threshold, and it is what converts pixel density into a viewing distance. |
| Field of view | How much of your vision a screen occupies, in degrees. Roughly 30 to 55 degrees suits desk work. Beyond that you turn your head to read the edges. |
| Aspect ratio | The proportion of a screen. 16:9 is standard, 21:9 is ultrawide, 32:9 is super ultrawide. Screen width is the diagonal multiplied by 0.872 for 16:9 and 0.922 for 21:9. |
| Clamp mount | A monitor arm fixing that grips the desk edge, typically accepting 0.4 to 3.5 in of thickness. The alternative is a grommet mount, which drops through a hole in the surface. |
| Joule rating | How much total energy a surge protector can absorb before it is used up. Higher means more events survived, not stronger protection per event. Surge protectors are consumables. |
| Power factor | The ratio used to convert watts to volt amps when sizing a UPS. 0.6 is the usual planning figure, so a 300 W load wants roughly a 500 VA unit. |
| Sound absorption | Converting reflected sound energy to heat inside a porous material. Panels absorb. They do not block sound passing between rooms, which is a mass problem and a different one entirely. |
Fuller explanations of the standards are on the standards page, and the arithmetic behind each dimension is in the calculators.