Median based on criteria

Hi there,

Im having a few issues trying to calculate the median in a document.

First up - Im trying to calculate the median on a set of parameters. I need for my median to be based by operations centre based on an audit score. For example the BIF median, the MIN median etc. This can be seen in the attached document in the tab GRAPHS. I have set up a basic formula but not sure what else i need to put in.

Secondly - Im having issues with the median formula when there is an N/A in the cell (as there is no input as yet). You can see in the main tabe AUDIT SCHEDULE AND DATA that i have set up column O to automatically assign a number based on column N. However if there is no score then an N/A is in cell O. This is fine - im just having problems when im trying to calculate the median.

Any help that can be provided will be GREATLY appreciated. I have attahced a sample document with some detail.