The code supplied above has the general right format, but does not produce a standard deviation or coefficient of variation.  The adapted code below has been tested against Excel formulas.  It uses the StDev.p rather than the sample version of N-1. 

SQR((ABS((C / C1-1) ^ 2 + (C1 / C2 - 1) ^ 2 + (C2 / C3 - 1) ^ 2 + (C3 / C4 - 1) ^ 2 + (C4 / C5 - 1) ^ 2 + (C5 / C6 - 1) ^ 2 + (C6 / C7 - 1) ^ 2 + (C7 / C8 - 1) ^ 2 + (C8 / C9 - 1) ^ 2 + (C9 / C10 - 1) ^ 2 + (C10 / C11 - 1) ^ 2 + (C11 / C12 - 1) ^ 2 + (C12 / C13 - 1) ^ 2 + (C13 / C14 - 1) ^ 2 + (C14 / C15 - 1) ^ 2 + (C15 / C16 - 1) ^ 2 + (C16 / C17 - 1) ^ 2 + (C17 / C18 - 1) ^ 2 + (C18 / C19 - 1) ^ 2 + (C19 / C20 - 1) ^ 2 + (C20 / C21 - 1) ^ 2 + (C21 / C22 - 1) ^ 2 + (C22 / C23 - 1) ^ 2 + (C23 / C24 - 1) ^ 2 + (C24 / C25 - 1) ^ 2 + (C25 / C26 - 1) ^ 2 + (C26 / C27 - 1) ^ 2 + (C27 / C28 - 1) ^ 2 + (C28 / C29 - 1) ^ 2 + (C29 / C30 - 1) ^ 2)

- ((((C / C1 + C1 / C2 + C2 / C3 + C3 / C4 + C4 / C5 + C5 / C6 + C6 / C7 + C7 / C8 + C8 / C9 + C9 / C10 + C10 / C11 + C11 / C12 + C12 / C13 + C13 / C14 + C14 / C15 + C15 / C16 + C16 / C17 + C17 / C18 + C18 / C19 + C19 / C20 + C20 / C21 + C21 / C22 + C22 / C23 + C23 / C24 + C24 / C25 + C25 / C26 + C26 / C27 + C27 / C28 + C28 / C29 + C29 / C30) /30) -1) ^ 2 * 30)) /30)

 / (((C / C1 + C1 / C2 + C2 / C3 + C3 / C4 + C4 / C5 + C5 / C6 + C6 / C7 + C7 / C8 + C8 / C9 + C9 / C10 + C10 / C11 + C11 / C12 + C12 / C13 + C13 / C14 + C14 / C15 + C15 / C16 + C16 / C17 + C17 / C18 + C18 / C19 + C19 / C20 + C20 / C21 + C21 / C22 + C22 / C23 + C23 / C24 + C24 / C25 + C25 / C26 + C26 / C27 + C27 / C28 + C28 / C29 + C29 / C30) / 30) - 1)

I'm most impressed with your work!  I'm still trying to figure out how it all works, since PDFs are relatively foreign to me. 1. When I load the indicator into a chart it appears that the C1, C2 etc. refer to the period of the chart.  So if the chart is weekly, the calculations are over the past 30 weeks.  Is there a way to get that data into a watchlist column?  The watchlist column appears to only bring in daily calculations.  I presume I could rewrite the PCF with C/C5 + C5/C10 etc. if that is the necessary way to get there.  2. Regarding the negatives, I presume you are saying that the way it is written is not a valid COV.  However, might it be more useful for trying to identify smooth momentum if I take the values starting > 0 ?  That would eliminate an overall negative value, but I'm not sure of the effect of negatives within specific periods.  Do you have thoughts on that?  Thanks again.   Lee 

I would like to write a PCF that would calculate the average return (percent change) for the last x periods, i.e. 30.  I would like to divide that average into the standard deviation of the returns of the last x perioeds, i.e. 30.  Is it feasible to do this with a PCF?   If so, can someone point me down the path to doing so?   

At http://www.traders.com/Documentation/FEEDbk_docs/2010/06/TradersTips.html#TT5 I find about 17 software programs that have implemented the Fractal Dimension Index, including StockFinder from the same article/issue Bruce referenced.  Most other vendors provide their script, which when I paste into their respective programs I see a similar pattern, except for StockFinder.   What gives?

The Fractal Dimension Indicator is apparently not a single entity, even when matching the parameters such as N and dates.  The Stockfinder 5 chart presumable taken from Erik Long bears little resemblece to the FDI as published daily in the Fractal Market Report by David Nichols (www.fractalmarketreport.com) or to the charts produced by Matt Trivisonno's Fractal Stock Grapher utility. ( http://www.trivisonno.com/fractal-stock-grapher)  It would be nice if you could make the other FDI's available so that we could back test all three, and perhaps others that are out there.  The Long article upon which the Stockfinder FDI is based gives some general guidance or prinicpals, but nothing specific enough for accurately implementing signals.

Is documentation available for the Fractal Dimension Indicator as to the formula used and suggested signals?  The indicator line is very different from the Fractal Dimension software I use, given the same parameters (N=30 and daily or weekly bars).  Fractal Stock Grapher doesn't provide alerts or screening, but the signals are uncanny.