A partner asked how many decateaspoons are in a US gallon.
Perfectly reasonable thing to ponder on a caturday afternoon.
I asked qalc:
> 1 gal to decateaspoon
1 gallon = 75.70823568 decateaspoons
She asked python pint:
[ins] In [8]: ureg.define("decateaspoon = 10 * teaspoon")
[ins] In [9]: (1 * ureg.gallon).to("decateaspoon")
Out[9]: 76.80000000000001 <Unit('decateaspoon')>
... Wait why are these different?
libqalculate defines 1 teaspoon as 5 mL.
Wikipedia agrees:
For cooking purposes and dosing of medicine, a teaspoonful is defined as 5 mL (0.18 imp fl oz; 0.17 US fl oz), and standard measuring spoons are used.[3]
The citation link is "retired" but is archived. It explains that the volume of a household teaspoon varies and should not be used for dosing medicine, and states:
A standardised teaspoon to deliver liquid medications holds 5 millilitres (ml) of liquid.
Ok so this feels like there's probably a US and metric variant of teaspoon. I normally refer to UCUM for unit facts, as they tend to cite all sources for their information.
Turns out yep, there are US teaspoons and metric teaspoons.
The US teaspoon derives from the US gallon, which... well, I'll let the UCUM specification explain:
The U.S. fluid volumes have been defined based on Queen Anne's wine gallon which was in turn defined exactly as 231 cubic inch. Although we used international inch, we are not sure what inch definition is actually used for defining the exact size of a U.S. gallon. However, the differences between the various inches are minimal, even when raised to the 3rd power (i.e., the difference between the U.S. inch and the British Imperial inch remains in the sixth decimal digit.)
tl;dr: I was today years old when I learned there is a metric teaspoon and a US teaspoon and they are ever so slightly different