Question regarding SMA

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I'm new to MQL4, and I'm wondering if someone can answer this simple question. I want to compare the value of the current SMA(20 bars) to the

previous SMA(20 bars).

Here is my code. Is this correct? I basically changed the shift value to 1:

if ((iMA(NULL,0,20,0,MODE_SMA,PRICE_TYPICAL,0)) > (iMA(NULL,0,20,0,MODE_SMA,PRICE_TYPICAL,1)))

return (true);

What is the difference between ma_shift and shift? Yes, I read the docs, but I am still confused.

Thanks!