Hello:

1 mill = $(1/1000) can be expressed as $(1/1000)/(1 mill).

How does 1 mill = $(1/1000) becomes $(1/1000)/(1 mill)?

\text{1\ mill\ =\ \frac{1}{1000}}

Divide both sides by the 1 mill.

\text{\frac{\cancel{1\ mill}}{\cancel{1\ mill}}\ =\ \frac{\frac{1}{1000}}{1\ mill}}

Since the left canceled out, you end up with:

\text{\frac{\frac{1}{1000}}{1\ mill}}

Are you using this for taxes? And like trying to work things backwards? I think there's probably an easier way to do it. For one thing, instead of using 1/1000 which makes it look all icky, you can move the decimal three places to the left. Like 26 mills would be .026. A mill is one tenth of a cent, or .001. That also isn't the only way to do it and isn't the way I do it.

One mill can also mean 0.001". Typical machinists talk. Thousanths is too hard to say.

Machinists and "financists" are not supposed to have things in common. That's like sacrilege or something. :D