[amibroker] Use calendar day rather than trading day

[hatizen]

Hi, 

I'm trying to find the growth percentage between close price today and 
close price 30 calendar days ago.

When i use 30 in the formular below, it returns the price as of 30 
TRADING days ago, not calendar days. What do i need to do to make it 
fetch the calendar day price? thank you

growth = (Close - Ref(Close, -30)) / Ref(Close, -30) <= 0.1;