error bars and standard deviation

hey, ive got a bar chart and i want to add an error bar to each bar to reflect its standard deviation. but at the moment excel will only let me change all of the bars so that the error bars are all the same for every bar in my chart. how do i do each one seperately? and which option do i choose so that i can type in the particular standard deviation for a particular bar?
thanks,
emily

Have you tried calculating the desired length of the error bars in the spreadsheet, then use the "custom" option to point to the range(s) containing those error calculations?