How to calculate a true average in Access?

[Anthony Flores]

My goal is to set Standard Test Times per Unit.
There are multiple Operations(10-12 depending on product type) performed during the production of each unit that are being tracked seperately (time wise).
Most are pretty simple such as,

Operation 10 total time / kit quantity = average process time for each unit at Operation 10.

My issue is that when I have multiple kits of the same product Access gives me the average of each kit and then give me the average of the average for my answer which can be off (greater) as much as 3 times the actual average. Most of the Operations can only be performed 1 unit at a time. There are 2 operations that complicate matters due to the ability to process 2 units at the same time as described below.

I can test units on 1 or 2 test fixtures. Each unit takes the same amount of time to test. But by using 2 test fixtures I can test 32 units in the time it takes to test 16 units on 1 test fixture. But I still need to know how long it would take to test each unit one at a time.
For calculating unit minutes during which multiple test fixtures can be used I want to do the following

Total time =(Process time * number of test fixtures)

Unit minutes = (sum of Total time)/ (sum of total units)

For all other process operations the calculation will be

(the sum of the minutes)/(sum of the units)= avg unit minutes

I can send either an excel spreadsheet showing what is going on or the Access datatbase.