I am not very convinced of this API, the variable `q` does not contain any reference neither to MKS nor to seconds in its args tree, despite being measured in seconds. The variable `day` is specified by a factor `86400` without specifying that it's relative to seconds.

I examined the `q` variable:
```
Quantity: 6.13837e+08 (0.0316228 {'time': 1})
commutative: True
+-Float: 613836514.946152
+-Unit: (0.0316228 {'time': 1})
  +-Float: 0.0316227766016838
  +-Dimension: {'time': 1}
    +-Dict: {time: 1}
      +-Tuple: (time, 1)
        +-Symbol: time
        +-One: 1
```
I would modify the `Unit` class, and make sure that you can pass a string, i.e. instead of
```
>>> u = Unit(1, Dimension({'time': 1}))
```
replace it with
```
>>> u = Unit('second', Dimenions({DimensionSymbol('time') : 1}))
```
This way: we know for certain that the numerical value of the quantity is expressed in seconds. Time becomes an instance of the DimensionSymbol class (i.e. 'time' is neither a string nor a symbol, I believe that logical meanings should be clear from types).