Lighting master slider

I have a built a fish tank LED lighting system which is run via 7 PWM channels of my Arduino Mega via an app called Blynk on a Samsung tablet.

I have sliders on the app which adjust each of 7 variables from 0-255. I would like to add a 'master' slider which will increase or decrease whatever the individual variables are proportionately. I can't however figure out the maths/algorithm.

Can anyone help on how I can make this happen?

Scaled multiplication. You have already chosen an implicit scale of n/256. So for example, 128 is half intensity because 128/256 = 1/2.

So multiply any value by the master, and then divide by 256. Example: master is set to 128, some channel is set to 128. So both the master and channel are at halfway. You have (128*128)/256 = 64.

Arrrrr. Thank you aarg. Was 4am here and couldn't wrap my tiny mind around it. Thank you.