December 1954 Popular Electronics
Table
of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
from
Popular Electronics,
published October 1954  April 1985. All copyrights are hereby acknowledged.

Maybe given the nature of newly published Popular Electronics, the
editors decided using a big word like "nomograph" might be a little
too out of the realm for use in a magazine seeking to appeal to
newcomers to the electronics field. It is a little surprising since
students of the day were quite accustomed to using this type of
a graph since computers still filled entire rooms and handheld
calculators went by a different name 
slide rules.
In fact, because of a familiarity with using a
slide rule,
people were more accustomed to having to shift decimal points to
the left or right first to do the calculation on a device that only
displayed values in a single decade range, and then to arrive at
the final answer after the calculation. That is exactly the skill
needed to use the nomograph.
I guess that people today  even engineers  would have a harder
time keeping track of powers of 10 than most reasonably skilled
high school math students of the 1950s.
E, I R, and P Chart
IF YOU know any two of the four quantities. voltage (E), current
(I), resistance, (R). and power (P), in a circuit, you can find
the other two by using this chart. Using the upper part of the chart.
just lay a straightedge between the graduations corresponding to
the two quantities you know, then read the other two quantities
where the straightedge crosses the corresponding lines.
Voltage, Current, Resistance, and Power Nomograph
For example, suppose the voltage is 100 volts and current is
30 milliamperes. The resistance is 3330 ohms (approximately) and
the power is 3.0 walls.
If the quantities you have are larger or smaller than any shown
in the chart, you still can find your answer. Move the decimal point
in each quantity to bring it within the range of the chart. In a
power figure. move the decimal point a multiple of three places;
in a voltage figure, a multiple of two places. In current and resistance,
the decimal point can be moved any number of places. Then, using
the lower part of the chart, lay your straightedge between the numbers
corresponding to the number of places you must move the decimal
point on the chart left or right to get the quantities you actually
have. Read along the straightedge the number of places you will
have to move the decimal point in each answer as given by the chart,
to get the proper decimal point for your actual problem.
For example, suppose that the voltage in the previous example
had been 0.01 volt and the current 0.3 milliampere. To go from 100
volts to 0.01. volt, we must move the decimal point four places
to the left. To go from 30 milliamperes to 0.3 milliampere, we
must move the decimal point two places to the left. In our answers,
we must move the decimal point two places to the left in resistance,
giving 33.3 ohms, and six places to the left in power, giving 0.000003
watt (0.003 milliwatt or 3 microwatts). END
Nomographs Available on RF Cafe:

Decibel Nomograph

Voltage and Power Level Nomograph
 Voltage, Current, Resistance,
and Power Nomograph
 Resistor
Selection Nomogram
 Resistance
and Capacitance
 Capacitance
Nomograph
 Earth Curvature Nomograph
 Coil Design Nomograph

Coil Inductance Nomograph
 Antenna Gain Nomograph

Resistance and
Reactance Nomograph
Posted July 1, 2011