Scale in Computer Assisted Drawing. 

There is no drawing scale when drawing in CAD.

There is only printing scale.

The size of the drawing on the screen has no effect on the scale that you use on your printouts.

"Scale" has no meaning in computer assisted drawing until print time.

Manual Drafting:

When drawing on paper by hand, printing begins with the first stroke of the pencil. The paper has to be chosen in advance so the plan will fit on the paper.

Not so in CAD:

All sizes and distances are specified using their full-scale values. 

A 10 foot object is drawn as a 10 foot object. 

When drawing in CAD, unlike in manual drafting, there is no need to determine in advance the paper size and drawing scale.

Print Scale:

Only at the printing stage, does scale need to be determined based on paper size and the plan to be printed.

Feel free to select a zoom level that will show the most detail, if that's what you need, or zoom out to show a larger area of your plan. Press the "Fit Plan to Screen" button to show the full extent of your plan.

Your plan, and the future print scale are not affected by the zoom level you use to draw.