All time high MA

Looking for someone who can code an simple indicator. 
plot a moving average x percent below the current all time high. 
it’s for indices and stocks. 
 

the calculation is 

x = 10 

so

all time high multiplied with 0,9

it has to be an MA, because I want to see price behaviour in the past at this level. 
 

x Must be adjustable. 
 

payment via PayPal only.