Rookie finance question: standard deviation

#1
Hi
Im kinda new to statistics and would very much appreciate some help.

I have finally understood the standard deviation formula and the reason behind every step/calculation. But..lets talk about stock market.

a) why does the stock market write s.dev in percentage? I had the impression that the normal way is to express s.dev with numbers, but with stocks its seems like they Always write percent? Why?

B) i can calculate the s.dev on a stock.
BUT i have a problem....lets say we gonna fins the s.dev for a stock for the last Three Days...we use the closing price each day. The first day the closing price is 10, then the second day its 12, and last day its 15.
Everything fine and I know how to do it.

But the problem is that this formula Only takes Into account the closing price..

I want to know how big the fluctuation has been each day. I want to be able to see:
Okey the closing price day 1 was 10...But the highest price during that day was 14 and the lowest was 6. So the daily course had a movement of +4 and -4 from the closing price (which was 10).

And day 2 the closing price (as i wrote) is 12...But highest point is 20 and lowest 7.
Etc..


I want to be able to answer the question:
Okey so If i invest in this stock day 4..what can i expect the Range of movement to be during the day?

And i dont get how i should calculate when the normal formula Only look at one variable each day (closikg price). I want to use two (high and low).


Anyone know the answer? Please help!!:)
And...please explain as you would do to a newbie:) Thanks!!:)