Welcome to T2W 73sand.
The formula is here, and there are also plenty of other formulae in case you feel adventurous.
http://www.mtsu.edu/~stats/dictionary/formula.htm#r
and this link has the formula already done in TradeStation language:
http://klub.chip.pl/tsfp/t-pb-R-Squared.html
R Squared in Metastock is:
pwr(corr(cum(1),C,5,0),2)
or
Pwr(Corr(Cum( 1 ),C,14,0),2)
or, for a smoothed version:
Mov(Pwr(Corr(Cum( 1 ),C,14,0),2)*100,14,S)
I believe that probably the most indepth analysis of this is in book The New Technical Trader by Chande & Kroll. I've not got the book though, so I cannot confirm this.