Zitalen,
"How can I set a numerical value to a tab or indent? I want them to be
EXACTLY the same"
Unlike in Word you cannot set a numerical value to a tab.
"and I don't want to use the snaps as they are too far apart?"
If the grey snaps are too far apart, click and drag one of them in the
direction you want and release the mouse button, if you dragged to the right
all markers will be further apart if you dragged to the left all the markers
will be closer.
Better is to set the tabs yourself by choosing the tab selector at the
beginning of the ruler, and then clicking in the ruler where you want the
tab stop to be placed.

"Why does a change I make to a line affect ALL lines in that placeholder?"
I know it's frustrating but there is nothing you can do about that. PPT 2007
has this problem solved, there you can use tabs and indents in exactly the
same way you would in Word, and they behave the same way.
"If a perfectly formatted line of text is copied into another placeholder,
WHY does the size (and often the type) change to something else???"
Normally pasted text takes on the formatting of the placeholder you put it
in, but upon pasting you will see a tiny icon called paste options, when you
click on it you can choose to keep the original formatting if you want.

If your text is in standard placeholders you can change the formatting in
the master of your presentation. View - master - slide master - select the
placeholder and format it the way you want. Close master view and text in
placeholders should be updated.
Luc Sanders
MVP - Powerpoint

Hi again Lena H!

I can't cure all your frustrations but one thing that helps a little is
knowing that putting a finger on Ctrl turns off the 'snap' and also allows
the carets to be moved to places they otherwise won't go! (for hanging
indents)

You can only (as far as I know) get numerical values with vba code. It would
look something like this:

Sub setindent()
With ActivePresentation.Slides(1).Shapes(2).TextFrame.Ruler.Levels(1)
.LeftMargin = 10
.FirstMargin = 40
End With
End Sub