How to Step Down a 500mV DC Reference to 450mV? Voltage Range is 0-1v DC

Alright you e-lectronic masterminds, I've got a predicament that I'm not quite sure how to solve. Basically, I need to take a DC voltage signal that varies between 0.1v and 1.0v several times a second (~20Hz) and step it down EITHER by a factor of 0.9, or by 50mV static. Is this something an Arduino can do, or am I barking up the wrong tree? If you were faced with the same situation, how would you go about doing this? Ideally, I'd like something pre-fabbed. If I could keep the soldering iron out of it, that'd be great.. Thanks!

The simplest way is a voltage divider. If you have two series resistors of 1k and 9k, you take the reading of the 9k and you have .9 of the input voltage.

The problem is that they do not make 9k resistors. What accuracy is required?

You could use a 10k potentiometer and set to a point with the ratio required.

Weedpharma

You could use a 10k potentiometer and set to a point with the ratio required.

Or 
Input ---- 680 ------1K POT ----- 8.2K -------
                        |                     |
                        A0                   GND

and how are you going to decide?