Facts, I don't have.
Wild unsupported supposition, with a helping of carefully crafted
cynicism.... There I have you covered. :-)

I suspect that it's some combination of:
Wildly optimistic marketing.
Subtle geometry that deviates from a simple prismatic solid.
Some perceptible volume added by the shape of the inside of the door and
the thickness of the seal.
In combination with the first one, they may be including the volume of the
waveguide all the way back to the magnetron.

May be impractical, but I wonder what volume you would get if you were able
to fill the chamber with water.....


My first rule of thumb for numbers written on the box: Assume they came
from someone that can't do math. (that may be my cynicism showing)
At the very least, they will be calculated to show the product in the most
favorable way possible and may be a complete fiction.

-Denny


On Sun, Jun 26, 2016 at 7:57 PM, IVP <joecolquitt@clear.net.nz> wrote:

> Hi all,
>
> recently I had to get a new microwave oven. I measured my old
> dead oven so I could get one of similar size, to fit various cooking
> containers
>
> It was 305 x 310 x 195mm, or 18.4 litres
>
> So I go shopping, armed with a ruler
>
> A local retailer had one advertised as 20 litres for $65. Sweet.
>
> But when I measure it in-store, I find it's barely 11 litres, and
> not even big enough to get a dinner plate in. Eh ?
>
> Long story short, I finally decide on one which is the same size
> internally as the dead one, 19 litres. But the box et al says it's 23.
> Similarly with every single other oven I looked at - all are stated
> to be much bigger than they actually are. If I'd not measured
> them I could have easily gone by the boxes and had to go back
> to swap for another
>
> I have the uneasy feeling I'm missing something stupidly simple
> but the maths is pretty straightforward. 30.6 x 30.4 x 20.8cm
> is not 23 litres, it's 19
>
> Do I have it right ? Surely it's right. If so, why the discrepancy ?
> It wasn't just this particular store either, or even the store's doing,
> the manufacturers write the capacity
>
> Joe
>
>
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