Aggregating a locked percentage value

So it seems that I have something that requires multiple steps to accomplish. I am trying to find the % of NOSHOWS from a table of instances and keep that number up on the dashboard. I am trying to do this by getting a count of all the instances by their unique ID, getting a count where [Status] = "NOSHOW", and then dividing the 2nd count by the first to get the % of no shows. However, this value doesn't remain locked if I look at data with other statuses because the total count will change so I want to know how I can lock a total for both all instances and NOSHOWs so the % can stay the same.