from Ebay (, offered at $4,999, October 2006 (no bidders) librascope balance computer

History:  Text.




  Pilots of the 1930’s were plagued by the complex problem of how to

Load their planes.  The weight of each passenger, each crew member,

Fuel, oil, cargo and bombs (in the case of military planes) had to be known and the total weight had to be distributed along the fuselage with precision so that the center of gravity of the loaded aircraft was exactly where it should be for take off.  If extra fuel was needed for a long flight, or if the crew compartment was changed, the pilot had to compensate by deleting or shifting a calculated amount of weight at some exact point along the planes longitudinal axis.  These calculations were carried out laboriously, by hand, with considerable room for error.  The loading process was slow and costly.


  A Mr. Lewis Imm took heed of this plight of the pilots and had the idea of developing a mechanical devise that would carry out loading calculations automatically.  Encouraged by local aircraft manufactures, Mr. Imm invented a rudimentary aircraft-loading balance mechanism, which he called a “LIBRASCOPE”, (“Libra”, being the zodiacal sign for the balance, and “Scope” meaning “instrument for viewing”).


  The prototype was constructed crudely in a garage with paper clips and rubber bands and packaged in an attaché case.  It worked very well.

Production models followed, still in attaché cases, but using machined cams and rods, and special springs.


  At the conceptual heart of the LIBRASCOPE, which we now know to be one of the very earliest aircraft ‘computers’, was a devise which Mr. Imm

termed a “moment sector” - - a balance beam linkage by which the sum of the moments along a fuselage was divided by the sum of weights to yield the center of gravity.  By tailoring moment sectors to aircraft dimensions, he could produce a LIBRASCOPE for any aircraft.


  By 1937, LIBRASCOPES had sold successfully enough that Mr. Imm founded a company to produce them – a company which he appropriately enough called “Librascope”.


  The importance of the LIBRASCOPE to early aviation is illustrated by an anecdote.  One Friday night in 1938, Mr. Imm was contacted by Howard Hughes, who wanted a LIBRASCOPE built for him urgently.  Mr. Imm delivered it the following Monday morning.  Howard Hughes proceeded to achieve fame by circumnavigating the globe in an airplane – in 91 hours, 8 minutes, and 10 seconds.  As reported in AVIATION   magazine of that year:  “Mr. Hughes kept an up-to-the-minute log of the weight center of gravity condition at all times during his phenomenal flight by means of a LIBRASCOPE”.


  The LIBRASCOPE thus has had a distinguished history – as has the company which continues to bear that name.





Item:  A Librascope Weight and Balance Computer.


U.S. Patent Number:  2,179,822

Filed:  April 17, 1937

Inventor:  Lewis W. Imm


Description:  The Original Mechanical Analog Aviation Weight and Balance Computer.  Computer Instrument is built into a portable brief case.  Brief Case material believed to be wood covered with black leather.

Computer dials may be made from one of the earliest form of plastics

(Bakelite).  Art Deco design styling.


Serial Number  1129      Type:  LC-1


Supporting Documentation:  Complete with Untouched Restricted Operations Manual.  Including matching serial number 1129.


Librascope Dimensions:  11”  High  X  18.5”  Wide X  3.5” Deep.

Frame Dimensions:          30”  High  X   37”    Wide X  5” Deep.

Weight 42.5 Total weight of mounting including Librascope.

Weight of Librascope is undeterminable (due to mounting).


Aircraft type:  Consolidated Catalina PBY – 5.


Condition:  Librascope and Operations manual Perfect Mint – Untouched.

                   Factory sealed.  No fade.  No imperfections.  No sun damage.

                   No warp.  No distortions.  No fingerprints.  No cracking or 

                   pealing.  Note:  Please ignore flash "Hot Spot" in photo.


Mounting:  Museum mounting.  Wall Mount Plaque. 

                   Hardwood.  Plexiglass.

                   Mounting include the addition of two photo’s.  One of the back

                   of the interior of the Librascope machinery and one of an

                   aviator using a Librascope.  Mounting also includes supporting

                   text and history of the Librascope.


Rarity:      Very Rare.  May be the only one in existence in Mint Proof

                   condition with matching Instructional manual.


Location of Manufacture:  Burbank, California, U.S.A.

Approximate Date of Manufacture:   1937 - 1938


An Analog Computer


Computer - A machine that calculates.

Analog computer - A computer that performs mathematical operations in a parallel manner on continuous variables. The components of the computer are assembled to permit the computer to perform as a model, or in a manner analogous to some other physical system.

Mechanical analog computer - An analog computer with input and output usually expressed as shaft position or degrees of shaft rotation.





The PBY series seaplanes and amphibians flown extensively by the Navy during WW II.  It is a twin-engine, parasol-mounted monoplane equipped with a flying boat hull, retractable tricycle landing gear and retractable wing-tip floats.

The prototype Catalina first flew on March 28, 1935. It was produced by Consolidated Aircraft Corp. in both seaplane and amphibian versions. Catalinas were also produced by Canadian Vickers, Ltd. and the Naval Aircraft Factory. Eventually, nearly 2,500 Catalina derivatives were built for the Navy.  Catalinas also were flown by a number of allied nations during and after WW II.