Hi - I assume you have read the full article in TASC by Thomas E Aspray. He does outline the formula also - as per below....

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Introduction

In analyzing the commodity markets, I use a series of approximately twelve technical studies which I

have selected after extensive historical research. If these studies are in agreement (uniformly bearish or

bullish), they determine how much emphasis to put on the daily studies.

For example, if the weekly studies are positive and the daily studies are negative, a short position would

be recommended only for scalpers, with close stops used. Conversely, if the daily studies were positive, a

larger position with wider stops could be taken. The studies I find most useful are those which combine

the price action with volume or open interest. One which I use extensively is the Demand Index,

developed by James Sibbet, which utilizes price and volume. I run this study in several different versions

over both the daily and weekly data.

The study calculates the Buying Pressure (BP) and Selling Pressure (SP) in the following manner for the

No Limit version.

If the prices rise: BP = V or Volume

SP = V/P where P is the percent change in price

If the price declines: BP = V/P where P is the percent change in price

If the price declines: SP = V

Because P is a decimal (i.e., less than 1), P is modified to make it greater than one by multiplying it by

the constant K.

For the No Limit version K=(3×C)/Va

where C is the closing price and Va is the Volatility average which is the ten-day average of a two-day

price range (highest high minus lowest low).

Also if SP> BP then DI = -BP/SP

In analyzing the Demand Index, I use several different levels of interpretation to help analyze the

underlying trend. They are:

1) Identify bullish and bearish divergences, i.e., determine whether the DI is moving with the prices or

opposite to the prices.

2) Extensively use trendlines and support/resistance levels on the DI, to determine important turning

points.

3) Separate the DI into BP and SP then determine whether the BP is above the SP (positive) or below it

(negative). I run an oscillator of the BP/SP which I call the Demand Oscillator