Mixture Desing - Desing with constant factor

[#1]

I like to create a design with 4 factors, in which one factor is constant and this should be taken into account for the 100% calculation. I get a result where the three variable factors are calculated to 100% and the constant factor is then over 100%. Can that be changed somewhere?

[#2]

Hi @Tom1,

Welcome in the Community !

I'm not really sure to have understood your problem, as it seems there is a mix/misunderstanding between quantities and ratio. Mixture designs involves factors that are linearly dependent of each other, and summing up to 1 (or 100%). 
In your case, I don't know in which situation you are :

1. You have a factor which has a fixed ratio, which means you could drop this factor in your design and indicates that the three remaining factors sum up to 100 - x % (x being the fixed ratio of your constant factor).
2. You have a factor that has a fixed quantity, which may not be a problem at all since other factors are ratios, so you can always adjust the total quantity of your mixture ingredients depending on this fixed quantity factor: for example in a formulation with 100g of ingredients, you can specify that 100% of the three mixture ingredients corresponds to a 90g mixture product, and add "on top" the fixed 10g quantity of your constant factor.

Can you please provide more context to be sure I understand your question ?
Is this answer already helpful or informative ?