Clearly 
There is a feature request that is close to this: Somme, moyenne, calculs dans les scènes
After this request goes off in all directions, it’s not very concrete, so I would create concrete feature requests.
Concretely for your request, two things are missing:
- Being able to perform a mathematical operation on a « scene variable »: addition, subtraction, multiplication, division
- Being able to inject a variable into an action « control a device ».