trouble with number(p,s) data type.

hi!
im using oracle8 and im having trouble using the number() data type. i just cant make sense of vat im doing wrong. can anyone explain vat p and s (precision and scale...as it says in my book) mean in number(p,s) data type?

suppose i have a column GPA. i need 1 digit before the decimal point and (say) 2 digit after the decimal point (for extra precision) because GPA cannot have higher value than 4.0
ie gpa number(1,2) then inserting value 3.45 gives this msg:
ORA-01438: value larger than specified precision allows for this column

so i alter the table: gpa number(2,1)
now that i insert 3.45, it rounds it off to 3.5, WHY?

so just to give it a try, i insert value 4.32 in gpa (not a valid GPA...but anyway) and upon selecting...it give 4.3
WHAT IS GOING ON HERE? can anyone explain plz?

also, can anyone plz tell me what are the maximum number of columns i can create in one table?

According to

http://download-west.oracle.com/docs/cd/B10501_01/server.920/a96540/sql_elements2a.htm#45723

You should use number(3,2)

I don't know the limit (but I'm sure that it's in the docs somewhere, most probably the concept or reference guide).
But anyway, I never reached this limit, the table with the highest number of columns I have seen was something like 50-60 columns, but that was poor DB design anyway (and I can't think of any example were having more then 50 columns would make sens)

thanx shammat!! its all clear now!