Mix and Yield variances

I have four quick questions to ask you relating to mix & yield variances. I hope you won’t mind 🙂

(1)
Standard mix is calculated where we need to take the proportion of the Kg used on one product divided by the total kgs used on all products such as:

Standard Mix = (Individual Std Kg / Total Std Kgs)

(2)
Actual Quantity Standard Mix (AQSM) is calculated such as:
AQSM = (Standard Mix x Total Actual Kgs)

(3)
Standard Quantity Standard Mix (SQSM) is calculated such as:
SQSM = (Standard Mix x Total Std Kgs)

(4)
Why do we use material Kgs instead of the material units produced in the calculations of mix & yield variances?

Am I correct?