We take the constancy of some things for granted. The speed of light, the love of a dog, the metric system. But!
Of course, a liter is a cubic decimeter (dm3); that's why a cc (cubic centimeter) equals an ml (milliliter).
But did you know that, from 1901 to 1964, a liter was not one, but rather 1.000028 dm3?
You could, as they say, look it up.
[Turns out that the liter is like the hour and the day. It it not really an SI unit; it is a non-SI unit that the SI will accept.]