RSI (relative strength index) in VBA

Hi all. I am wondering if anyone has the knowledge here to program RSI via VBA in Excel? I am able to do it without VBA, but it is time consuming and it takes up a lot of space and it just isn't it. Here is the description of what RSI is and the formula needed to calculate it:

http://stockcharts.com/school/doku.p...ngth_index_rsi


Can anyone do this? If so, please give me some pointers as to how to start. I have no clue how to program the "average gain" ...I am guessing it is a loop but how does one do it? Seems so complicated!