There is no such thing as a 3.5 inch floppy disc.
The term 3.5 inch floppy disc is in fact a misnomer. Whilst the specification for 5.25 inch floppy discs employs Imperial units, the later specification for the smaller floppy discs employs metric units.
The standards for these discs are ISO/IEC 8860-1:1987 (double density), ISO/IEC 9529-1:1989 (high density) and ISO 10994-1:1992 (extra-high density); all of which specify the measurements in metric. These standards explicitly give the dimensions as 90.0mm by 94.0mm.
In most countries, the national standard is simply derived from the ISO standard. In the U.S., however, the applicable standard is instead ANSI X3.171-1989. That, too, specifies the measurements in metric, though. It specifies the catridge dimensions as 90.0mm by 94.0mm by 3.3mm and the diameter of the magnetic disc material itself as 85.80mm.
If you have a floppy disc catridge that does not measure 90mm, then you have one manufactured by someone that is not careful about manufacturing tolerances. (And you should beware. If their product isn't up to specification in one area, it may not be so in others.) If the disc measures 3.5 inches, then it is the wrong size. 90.0mm is 3.5433 inches.
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> inches. When I measure my floppy disks to the nearest 1/32 of an inch, the
> dimentions are 3 1/2 in. by 3 5/8 inches. Thus one side is truly 3.5 inches.
> Some prometric websites say that instead of 3.5 inches it is really 90 mm,
> however my disks measure 89 mm x 93 mm. It is the opening to the floppy drive
> bay that is 90 mm wide (the disk has to be slightly smaller or else it won't
> slide into the drive)! Prometric people need to get the facts straight if they
> are to be credible to nonmetric people.
>
> Likewise the diagonal measure of computer monitors and TV screens are still
> stated exclusively in inches in the USA, even though the dot pitch is stated in
> mm. Since the dot metric is stated in metric, I wonder why the diagonal measure
> is not also stated in metric. I guess it is because people don't pay much
> attention to the dot pitch except when comparing specs, but the diagonal
> meausure is something they visualize when they see advertising.
>
> Trade Name!
>
> It's just a trade name. Just like a half-inch pipe is not really a half
> inch nor is a 3.5 inch floppy really 3.5 inches.
>
> I have an idea. Why don't you take the pot back to the shop you bought it
> from or call them on the phone, explain what you did and ask them how a 2 L
> pot can be called a gallon pot! Then report here. I'd be surprised to read
> clerk's answer.
>
> BTW. when you measured it as 2.25 L, were you filling it to the rim with
> something? If you were, that is wrong. Flower pots are never filled full.
> There has to be some space for debris and watering. That may in fact be
> meant to be a 2 L pot.
>
>
