Steve Taranovich examining an Apollo Service Module Engine at NASA White Sands. The Gerber Scale sped up designs like this to meet President Kennedy’s goal to get a man on the moon by the end of the 60’s decade (Image courtesy of Loretta Taranovich)

Back in the 60s, the Gerber Scale was quite a unique engineering instrument that enabled a new idea in the field of computation before computers came onto the scene. This was a manual and mechanical device that helped engineers immensely in that era.

The Gerber scale would perform computations directly on graphs and curves. The device was critical for reading, plotting, and interpolating on a graph in the days when plotter/paper graph printouts were popularly used.

During the birth of the space program at NASA, there were no computers of calculators available for engineers to simplify their calculations and charts/graphs. NASA engineers used the Gerber scale in the 60s for such things as pressure ratio from navigation, center of gravity, spacing rivets, laying out an airfoil section, and the power ratio of two curves, just to name a few.

Multiplication and division of a length by a number can be done as well as finding the peak of a curve. See the original Gerber Scale Application and Instruction Manual by Joseph Gerber, Chairman, Gerber Scientific for many more uses.

Ray Melton, an engineer who worked at NASA White Sands in the early days of the space program, used the Gerber Scale in his Rocket Engine-related work. Figure 1.

Figure 1 Ray Melton used this Gerber Scale for his work in the Rocket engine area at NASA White Sands Test Facility (WSTF) back in the early 60s. (Image courtesy of Loretta Taranovich)

The Gerber variable scale has a slider and a logarithmic scale is imprinted on its baseplate. The uniqueness of this amazing tool is a ‘CPU-like’ device in the form of a triangular shaped spring which has 100 calibrated coils, of which every fifth is blue-green in color, every tenth is red, and all others are white. Figure 2. 

Figure 2 The Gerber variable scale resembles a slide rule, but the similarity is only superficial, since the basic principle behind the two is pretty much completely different. Although this variable scale does have computational capability, it functions more like a divider, so it would be more appropriate to be placed in the category of a measuring device. (Image courtesy of Loretta Taranovich)

There is an indexed round coil spring that enables easier reading of the coils of the triangular spring. One end, of the two springs, is attached to the slider while the other end is attached to the left block of the baseplate. These will simultaneously extend when the slider moves from left to right and also will contract when moving back to the left as can be seen below in Figure 3.

There was a hex wrench included with the Gerber scale to adjust the friction between the slider and the sliding rail which prevents being pulled back from the desired stop position by the force of the spring. These linear springs follow Hooke’s Law; the coils will be equally spaced with respect to a slider stop position as shown in Figure 3.

Figure 3 These linear springs follow Hooke’s Law; the coils will be equally spaced with respect to a slider stop position (Image courtesy of Loretta Taranovich)

The Gerber Scale was used by engineers for linear interpolation/extrapolation of plotted data points without the need for any time-consuming computations. The base plate has a logarithmic scale which enables this device to be used on graphs or plots that have logarithmic coordinates. The Gerber Scale can also be used for a precision spacing divider for up to one hundred points!

Back in the 60s, many time curves were plotted, but needed to be re-plotted as a family of curves or a curve family multiplied by constants. Figure 4.

Figure 4 Curve “a” is drawn and the Gerber Scale plots a family of curves with values of 0.2a, 0.4a, 0.6a, 0.8a, and 1.0a. (Image from Reference 1)

To obtain the family of curves, the Gerber Variable Scale is placed along any point x parallel to the ordinate with the 0 coil at y=0 and the 100 coil at curve a. Next, mark off points at 20, 40, 60, and 80 coils as seen with the four coils below curve “a” in Figure 4. Then move the instrument to other stations x and repeat the procedure. Finally, draw a curve through equal % points on each of the four curves below “a”. It can be seen that a graph grid is not necessary once this image is completed.

Unfortunately, the Gerber Scale is no longer in production, but the Gerber Scientific Company is still in business.

The Smithsonian National Museum of American History, in Washington, D.C., has a Gerber Scale and instruction manual on display.

References

1 Gerber Scale Application and Instruction Manual by Joseph Gerber, Chairman, Gerber Scientific

2 Nathan’s Possibly interesting website