please any body help me for the calculation of total "if(ISERROR)" formula

[tahseen]

I have a spreadsheet which is divided into 4 weeks for the year. Numbers are entered into the NEG column, and the #CHRT column, and the % column is calculated, along with the TOTAL column (N).


Problem #1:
If all 4 weeks are not filled in, the total column does not display. I need it to average whatever % columns are there - for instance, the below total should be 78.57%, but it's blank.


I need each sheet to work like this - each sheet's calculations are slightly different as defined in text at the bottom of each sheet. Currently the total fields only work if all weeks are filled in - that's the problem.
Currently the % columns and total columns are locked and should not allow user to type in any calculated field.