Welcome to the world of graphic design. First time visitor, are you? "p0" is nothing -- it's "0p0", and that stands for zero pica's and zero pica points.

The online help for "measurement units" answers your question: http://indesignsecrets.com/change-measurement-systems-on-the-fly.php

To change your default unts:

Close all open documents.

Open InDesign Preferences

Go to Units & Increments

Set Horizontal and Vertical Ruler Units to desired option (such as Inches)

Click OK

That will set your units for all future documents.

Existing documents will have to be changed when opened.

Personally, I use Points, set to 72 pts per inch. I feel I have more control over object size and placement.

I do not use picas, so I cannot comment on how useful they would be. 6p0 would be equivalent to 1 inch, or 72 points.

I use points beacuse:

• It is the same unit of measure for the text (font size in points)
• At 72 points per inch, it is roughly equivalent to the pixel resolution on images (72 pixels per inch).
• I can adjust things by points, where each point equals 0.01389 inches. It is easier to adjust by adding 1 or more points than by large decimals of inches, even though the dialog boxed can do the math for you.
  • If you need to set something as a scale in inches, you can still enter that number into any field, and the field will convert it for you,
  • Enter 1.25 in, and you get 90 points.
    

Still, it is my personal preference. It is not the only way to do things.

-mt

PS: When you set the preference using the rules, you are setting the document preference. Though, each ruler can be different.  For instance you can have inches vertical and picas horizontal.

awesome...thanks, MT.Freelance -- you're the only one who ACTUALLY answered the question. All the rest of you art-**** talkin' about picas where missing the point.

After closing all docs, I was finally able to change the preference -- (BTW: that seems like a bug)

It's not a bug, it's by design.

I love this behaviour. I set up everything to my taste long ago; now when I create a new document, I have sensible defaults assigned to virtually every fuction. Much better than creating a template or something and having to open that every time!

Please run the InDesign application and do not create any new document and go to Preferences>>>Units & Increments and set the  unit as inches  in Horizontal and  Vertical fields and press ok , from now onward you will get inches by default in the new document set up window