I need a new feature adding to my wordpress plugin

i have a wordpress plugin that needs an additional feature added to it, at the moment the front end user view shows a fixed value of 1 for all users across the entire site, what i need is to able to change this value by creating a new tab in the admin area where i can change it in the admin and it shows the same to the users in the front end, also i have a details page that also does it's calculations based on this value and i need these calculations to change depending on what vale is entered by admin.