What is a jet (unit) shown in Windows 10 calculator? [closed]

From Windows 10's calculator:

What is a "jet" (physical unit)?

And why does it equal 480 knots or 888,88 km/h, if a jetliner's cruising speed is around 950 km/s? Or why does it equal 0.73 M, if a regular jetliner's cruising speed is 0.85 M?

• +1 for cursing speed stated in km/s. That's actually plausible. Mar 1, 2019 at 16:21
• I think "950 km/s" is a typo; surely the jet isn't moving at 950 kilometers each second. Mar 1, 2019 at 19:53
• European or African? Mar 2, 2019 at 0:54
• Thank you all for all your enlightening comments. It is really a nice thing that such a silly (after all) question made that number of people laughing and happy! :> There's one thing that I always had trouble to understand. If this question is OT (while it clearly is, since it asks about non existing unit) why does it have so many upvotes and two, quite professional answers? :> Mar 2, 2019 at 14:43

It is not a unit. It is just Microsoft trying to be funny. Or to convey an idea of the magnitude.

Thanks @Jackie for pointing out that around March 2019, Microsoft has released this calculator as open source under MIT license. It is available in this Github repository. The source code sheds light on the definition of these pseudo units:

Description in ./src/Calculator/Resources/en-GB/Resources.resw:

<data name="UnitName_JumboJet" xml:space="preserve">
<value>jumbo jets</value>
<comment>A jumbo jet (eg. Boeing 747), used as a
comparison measurement unit for length.
(...)
</comment>
</data>
...
<data name="UnitName_Jet" xml:space="preserve">
<value>jets</value>
<comment>A jet plane, used as a
comparison measurement unit for speed.
(...)
</comment>
</data>


/*categoryId, UnitId, factor*/
static const vector<UnitData> unitDataList = {
...
{ ViewMode::Speed, UnitConverterUnits::Speed_Turtle, 8.94 },
{ ViewMode::Speed, UnitConverterUnits::Speed_Horse, 2011.5 },
{ ViewMode::Speed, UnitConverterUnits::Speed_Jet, 24585 },
...
{ ViewMode::Length, UnitConverterUnits::Length_Paperclip, 0.035052 },
{ ViewMode::Length, UnitConverterUnits::Length_Hand, 0.18669 },
{ ViewMode::Length, UnitConverterUnits::Length_JumboJet, 76 },
...
};


Apparently these definitions assume length in meter, and speed in cm/s. Thus, in Redmond the typical cruising speed of a typical jet is 478 knots. We also learn that Clippy is 3.5 cm tall.

888.88 km/h are very, very lucky speed digits for Chinese people. Any aircraft manufacturer or airline would benefit from promoting this cruising speed...

• It just needs Clippy™ waving itself around for complete & utter uselessness. Mar 1, 2019 at 20:22
• @FreeMan - It almost does - look at the Length setting - for small numbers it gives you the units in "paperclips". Mar 1, 2019 at 20:58
• @DarrelHoffman ugh... I was kidding!!! Mar 1, 2019 at 21:01
• @FreeMan: so was Microsoft. :-D Mar 2, 2019 at 23:07
• I will do my best to refrain from down-voting simply for the presence of Clippy. :shudder: ;) Mar 5, 2019 at 15:41

Why does it equal 480 knots?

480 KTAS is the typical cruising speed of wide-body jetliners. KTAS means knots true airspeed (unaffected by wind). This is different from the ground speed passengers are used to (affected by wind).

Jet (unit) is not a standard unit as @bogl pointed out.

For example, the Boeing 777 Wikipedia article lists the cruise speed as:

Cruise Mach 0.84 (482 kn; 892 km/h)

Why does it equal Mach 0.73?

The speed of sound at 20°C is 343 m/s, and 480 knots is 247 m/s, so the Mach number (a ratio) is ~0.73. The higher you go, the colder it gets, and the slower the local speed of sound becomes, that's how 480 knots can end up being Mach 0.85 for jetliners.