move servo to a fixed distance

I am a beginner at arduino, I have to move a robot to a fixed distance using servo (the robot has wheels and can move either left or right, not vertically). I have read
http://forum.arduino.cc/index.php?topic=65988.0
http://forum.arduino.cc/index.php?topic=5701.0

but to no avail. I know normally used time on widths are 1-2 ms and I can move my robot to either extreme left or right. But what if I want to move the machine to an intermediate distance? if machine can move 3 metres to extreme left and right, what if I want the machine to move 2.3 meters?

Are you using regular servos or continuous rotation servos?

I find it hard to imagine motion of 3 metres with a regular servo. And you can only control the speed and direction but not the position of a continuous rotation servo.

...R

As far as I know, the only way to do that with a servo is with a continuous rotation servo, because most servo can do 180 degrees (more or less), so you have "left" and "right"
But if you want to stop a continuous servo, you'll need an encoder or something to identify the position.

if machine can move 3 metres to extreme left and right, what if I want the machine to move 2.3 meters?

You will need to use some position determining method external to the servo operations.