**Note** - from June 24th 2009, this blog has migrated from Blogger to a self-hosted version. **Click here to go straight there**.

A
couple of folks have e-mailed and pointed out that the **Commodity
RantCharts** generated a 'Division by Zero Error' when they tried to
chart the **Australian Dollar**.

This was caused by the fact
that the Commodities chart only uses the current front-month futures;
at the start of the chart data (80 trading days ago) the current
front-month did not trade. This means that in the data, the high and
the low are the same - which causes a hairball the formula for the %R
for the very first observation on the chart (the rest of the data is
perfectly fine, and so is the final chart).

The formula is

%R = 1-(C-L_{14})(H_{14}-L_{14})

where

H_{14} is the highest high in the last 14 periods, and

L_{14} is the lowest low in the same timeframe.

If the two are equal (which by chance they are, in this dataset) it produces a divide by zero error. I've changed the code so that it simply starts the %R one period further on if it encounters this problem.