Three Questions about Dimensions

Setup:
- New Drawing: Letter size
- Drawing Prefernces - Units Tab
.. Main Drawing Unit = 1 inch
.. Format Decimal
- Drawing Preferences - Dimensions Tab ... shown below ...



- Draw a 100 x 100 Rectangle
.. Click Line > Rectangle
.. First Corner = 0,0
.. Second Corner = 100,100

- Draw the Horizontal & Vertical Dimensions as shown below ...



Question 1:

What do the the dimensions mean?
.. 100 inches by 100 inches or what?

Question 2:

How to get the dimensions to display in inches?

Question 3:

Under Drawing Preferences
What is X & Y Spacing?
When I change it I see no visible change on the drawing

Thanks for any help.

OK, I think I have this figured out... after some experimentation.

Options > Drawing Preference > Length Factor should be set to 1.
So if you paper is 8.5x11 inches...

And you draw a rectangle 8.5x11...

And you set Options > Drawing Preference > Length Factor = 1
And you draw a horizontal dimension along the top from the left corner to the right corner
The Dimension will read 8.5000 ... aka the width in inches

If you change the Options > Drawing Preference > Length Factor to be 2
The Dimension will read 17 ... 2 times 8.5

Wasn't obvious to me by inspection... until I experimented some with Dimension options.
I'm sure it is clear somewhere in the doc's but after an hour+ of reading & Googling I just decided to start experimenting over and over... and after awhile I got it.

Regarding... Question 3:

Under Drawing Preferences
What is X & Y Spacing?
When I change it I see no visible change on the drawing

I still haven't had any luck finding out what that does... but I'll bang on it some more until I get or until some kind soul gives me a tip.

X and Y Spacing are the "Grid marks" when you want them shown.  The larger the number, the fewer and further between Grid marks.

Say UNIT = INCH

At 10=X and 10=Y, grid marks will occur every 10" x 10" and the distance between each adjacent pair will be 10".

At 1=X, 10=Y there will be 1" x 10 marks in the X direction and 10" x 1 mark in the Y even though, zoomed out, there are lines of intersection only every 10".  Zoom in to see the smaller "X" marks.

A simple LINE from 0,0 to @10<45, then ALIGNED Dimension from ENDPOINTS makes the point clear in the 1=X and 10=Y.