The Data Scaler Proportional Rule: a Gerber Variable Scale clone

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The Data Scaler Proportional Rule
A Gerber Variable Scale clone

This article was originally published in the autumn 2016 issue of the UKSRC Slide Rule Gazette.

The Gerber Variable Scale (GVS), described here, is a thing of beauty and elegance, admirable for its ingenuity and craftsmanship. It is also a “one of a kind” device, or so I thought until my unexpected sighting on eBay of the “Proportional Rule” made by the Data Scaler corporation of Westfield, Massachusetts.

The Proportional Rule by the Data Scaler Corporation

Click photo to enlarge

$Bottom side, with temperature and fractions of an inch conversion tables$
Click photo to enlarge

One look was enough to identify this device as a GVS knock-off. It has exactly the same structure and mechanism, albeit with slight differences in construction details. I’ve never heard of it before, so you can bet I made sure to win the auction. Once delivered, I could compare it to the original GVS in my collection. Both devices employ a triangular spring to provide a stretchable calibrated linear scale, and a round spring to carry the six numbered discs that follow the expanding scale. Both have the same three numeric scales and a cursor over them. Same device... yet different.

Gerber Variable scale (front) and Proportional Rule

Click photo to enlarge

There are some small differences in the mechanical design:

Both devices are the same 12 inches in length, but the Data Scaler Proportional Rule (DSPR) is larger, due to its greater height and width. The added height serves no purpose, and could easily have been eliminated with a little design effort; the extra width accommodates an added 10 inch ruler at the rear edge. The overall effect is that the DSPR feels much bulkier than the slim GVS.
The cursor on the DSPR is a traditional framed cursor as seen on most slide rules; the GVS uses a rather understated narrow frameless piece of Plexiglas, and is arguably harder to read.
The three calculation scales on the DSPR use black markings on a white background, which is perhaps easier on the eyes than Gerber’s elegant white-on-black.
The round spring in the GVS is built around a round guiding rod that ensures its position; the DSPR lacks this rod, using a groove in the baseplate to keep the spring in place (see photo below). Both systems seem to work equally well – two divergent solutions to the same problem.

Gerber Variable scale (front) and Proportional Rule mechanisms, with plastic cover removed

Click photo to enlarge

And then there are the differences in quality of manufacture:

The discs bearing the scale numbers on the DSPR are misaligned to the spring and to each other, and the numbers printed on them are not properly centered (see photo). The GVS has none of these flaws.
The main spring of the GVS stays straight even when fully compressed; the DSPR spring becomes wobbly at that point.
All screws on the GVS use metal or rubber washers under their heads, unlike those on the DSPR.
The transparent protective cover running along the device is evidently made of different plastics; the one on my GVS is clear and true, while the one on the DSPR has yellowed and warped, so much so that it has torn itself off its retaining screw at one end.
The bottom and back facing parts of each turn of the triangular spring are a matte black on the GVS, making them practically invisible; on the DSPR they have enough white showing – perhaps from an artifact of the painting process of the front faces – so they interfere with the illusion of a “disembodied” scale.
The cursor glass (actually, plastic) on this proportional rule does not fit its frame – I can only surmise this is the result of a poor repair job.

Looking beyond these details, the Gerber device has that feel of quality of design and manufacturing that we engineers can detect instantly; the Data Scaler Proportional Rule implements the same invention with a coarser and clearly inferior workmanship. But then, that’s not unusual for a knock-off (see my comparison of the Odhner and Felix pinwheel machines).

Gerber Variable scale (front) and Proportional Rule – detail

Click photo to enlarge

    The story behind the Proportional Rule was at first elusive. There is no mention of it anywhere I could find. The only online information about the Data Scaler corporation – unearthed by Rod Lovett – tells us it was incorporated on April 3, 1968, and went through Involuntary Dissolution on January 10, 1979. Its address – also noted on the back of the rule – was 626 Western Avenue, Westfield, Massachusetts. Significantly, this is about 30 miles north of Hartford, Connecticut, where Gerber Scientific had its headquarters.
    Enter David Gerber, Joe Gerber’s son (and author of the fascinating biography “The Inventor's Dilemma: The Remarkable Life of H. Joseph Gerber”, which I can strongly recommend). David informs me that the clone was made by his father’s former sales director, one Bud Colligan, who had resigned and gone into business for himself immediately after the variable scale patents had expired.
    Google street view shows the 626 Western Avenue address to be a modest family house in a residential area; the address, and the same phone number found on the back of the rule, are listed today in US public records as belonging to a Charles J Colligan, aged 91. This could be “Bud” Colligan himself, or a relative of his (and the age certainly hints at the former guess). More online sleuthing shows that the company’s president and secretary was Rita K Colligan, aged 94 today, and its treasurer was Terrence C Colligan, aged 65, both of them formerly resident in the aforementioned address. These must have been Bud’s wife and son.
    All these snippets of information show us that Data Scaler was a low key operation, headquartered in its founder’s residence. Evidently it did not transcend these modest beginnings, and went out of business after a decade. Perhaps some engineers found its product of use back in the day; certainly I find it a valued addition to my collection!

Exhibit provenance:
eBay, from a seller in Massachusetts.

More info:
Here are two pages from the manual of the Proportional Rule, which were found by David Gerber: Page 1 Page 2.

And another manual, with a different company address, contributed by Jim Bready:
Page 1 Page 2.

The Data Scaler Proportional Rule

A Gerber Variable Scale clone