Lycoming Horsepower Calculation?

I'm looking at the Lycoming Operators Manual Performance Data Chart for for
the O-360-A1A....(page 3-51 in my manual). And after looking at this for a
few min i need a beer.

Does anyone know of a formula that covers this chart calculation...?

I want to find the horsepower based on altitude, rpm, manifold pressure,
and air inlet temp...just like the chart shows.

I have a homegrown engine monitor that i fly with and want to add the calc
for percent horsepower.

thanks,

Mark
N515MD Mustang II
Raleigh, NC.

The best thing I have found for doing this is a circular sliderule sold
by Far West Aviation called the Power Wheel.
This thing is pretty neat. Read about it he
http://www.farwestaviation.com/about.html

It condenses all the hard to read data from the graphs in the Lyc
engine manual onto a circular scale
that will give you the percent HP, including altitude, temperature,
RPM, and M.P. It also gives a leaning
recommendation base on their experience with detonation. They give a
very extensive seminar of the
topic. My only gripe is that some of the printing on my Power Wheel is
a little muddy. Maybe I just got
a less than perfect one. They have a 100% satisfaction guarantee so
maybe I will call them up and see if they
are all printed that way.