how to control servo's stopping point?

I recently purchased a servo https://www.sparkfun.com/products/10189 and am wondering how to write a code to start and stop the servo at certain points. Here is what I would like to do...

Using an arduino UNO:

when you power up the UNO the servo will find the "center" and stay there
when a simple pushbutton Momentary Pushbutton Switch - 12mm Square - COM-09190 - SparkFun Electronics? is pushed once the servo would turn 90 degrees
when the button is pushed the second time it would rotate 90 degrees further (to the 180* point from center)
when the button is pushed the third time it would rotate 90 degreees further (to the 270* point from center)
when the button is pushed the forth time it would return back to the center position.

thanks for your help

when you power up the UNO the servo will find the "center" and stay there

Without extra hardware, that is never going to happen.

Hint: it isn't a servo anymore, despite what the seller tells you.

I think, under UK law, you'd have a very strong case for a refund.

Without extra hardware, that is never going to happen.

Hint: it isn't a servo anymore, despite what the seller tells you.

I think, under UK law, you'd have a very strong case for a refund.

So what you are saying is that I have the wrong type of "servo" for what I want to accomplish?

So what you are saying is that I have the wrong type of "servo" for what I want to accomplish?

I don't know, I haven't seen your spec.

is this what you want to see?

So what you are saying is that I have the wrong type of "servo" for what I want to accomplish?

Pick up the front of a bicycle. That front tire is a continuous rotation device, like your servo. Mark the "center point". Take a picture of where you marked. Then, we can talk about how to do the same thing with the not-a-servo that you have.

is this what you want to see?

No, I want to see your spec

the line i made runs perpendicular with the white plastic arm

the line i made runs perpendicular with the white plastic arm

That's nice.

just in case you haven't figured it out by now I'm a beginner so any advice would be appreciated!!

You've been here more than a month - any details of what you want to achieve would be appreciated.

It's a continuous rotation servo. There is no center point. There is no 0 degree mark, either. All such capabilities have been removed from that servo, to make it a continuous rotation servo. All that you can do with that "servo" is change the speed and direction that it rotates.

thanks PaulS

If uou need a servo that rotates more than 180 deg and is still a servo, then you might look at the sail winch servos.

PaulS:
It's a continuous rotation servo. There is no center point. There is no 0 degree mark, either. All such capabilities have been removed from that servo, to make it a continuous rotation servo. All that you can do with that "servo" is change the speed and direction that it rotates.

Actually they do a disservice and are misleading even calling it a servo. It's an ex-servo, it no longer represents anything that a servo controlled motor would share with it. It should be called what it has become sense being modified:

It's a bidirectional variable speed geared motor drive that is controlled by a pwm pulse.

From a SparkFun customer:

"If this were a servo motor, it would take a set point and adjust its position to be at the corresponding location, using internal feedback. If this is a continuous rotation motor, it takes a set point and scales its speed depending on that set point, but there’s no closed loop control, so it’s not a “servo”. This device may very well be in a package typical of servos and may even have been a servo before someone broke the feedback loop, but it’s not a servo if it’s continuous rotation, open-loop control."

Lefty