Description
This Signal Corps Scale ML-137 is a specialized military meteorological plotting accessory associated with the Plotting Board ML-55. For collectors of U.S. Army Signal Corps equipment, meteorological instruments, field artillery support gear, plotting-board accessories, and dated military technical equipment, this is a strong small-format reference piece tied to the practical work of military weather observation and wind-data plotting.
The ML-137 Scale belongs to the broader family of Signal Corps ML-series meteorological equipment. Meteorological equipment references list ML-55 as a Plotting Board, ML-87 as a Plotting Board Scale associated with ML-55, and ML-137 as a related Wind Scale within the same ML-series plotting and wind-data equipment group.
The Scale ML-137 and Plotting Board ML-55
The Plotting Board ML-55 was used in military meteorological work connected to pilot-balloon observation and wind plotting. A Field Artillery School thesis describing meteorological equipment explains that the ML-55 plotting board used a chart with a protractor, north-south grid lines, and a celluloid-covered working surface. Observations could be recorded on the celluloid, erased after use, and used to plot the horizontal path of a balloon. The same source describes wind speed and direction being read directly by means of scales on the special protractor furnished with the board.
A 1945 Signal Supply Catalog reference identifies Scale ML-137 as being similar to ML-87, except that the protractor portion was subdivided into 10 divisions. The same catalog reference describes it as used with, but not part of, Plotting Board ML-55, and used concurrently with ML-87.
For collectors, that gives this item added appeal. It is not a general drafting ruler or commercial measuring scale; it is a specific Signal Corps meteorological plotting accessory connected to the military systems used to process balloon observation data, wind direction, and wind speed information.
What This Scale Was Used For
As a Signal Corps Scale ML-137, this item was used as a plotting and measuring accessory for military meteorological work associated with the ML-55 plotting board and related ML-series wind plotting equipment.
In practical collecting and historical-reference terms, a scale like this is especially relevant for:
- Plotting Board ML-55 equipment displays
- pilot-balloon observation and wind-data plotting collections
- U.S. Army Signal Corps meteorological equipment research
- field artillery meteorological support displays
- Signal Corps technical equipment collections
- military plotting-board and protractor accessory collections
- museum displays focused on weather observation and fire-support data systems
This makes it useful not only as a collectible item, but also as a supporting piece for anyone studying how military meteorological sections converted observation data into usable wind information.
Historical and Technical Interest
Military meteorological equipment played an important support role in field operations, particularly where wind data affected artillery, aviation, balloon tracking, and weather forecasting. The ML-series equipment group included instruments such as barometers, anemometers, balloons, theodolites, plotting boards, wind scales, and related support tools, all intended to help military personnel gather and interpret weather information in the field.
The Scale ML-137 is especially interesting because it represents the smaller technical accessories that helped make the larger plotting-board system useful. While the plotting board itself was the primary working surface, scales and protractors were essential for reading, transferring, and interpreting plotted data.
For collectors and historians, this scale is especially relevant to subjects such as:
- U.S. Army Signal Corps meteorological equipment
- Plotting Board ML-55 accessories
- ML-series military weather instruments
- pilot-balloon observation equipment
- field artillery meteorological support
- wind direction and wind speed plotting
- World War II-era and early military weather-service equipment
Because it is a specialized accessory rather than a common manual, uniform item, or vehicle part, it adds strong technical depth to collections focused on the support systems behind military operations.
About This Scale
This listing is for a Signal Corps Scale ML-137 for use with Plotting Board ML-55.
It is especially well suited for:
- U.S. Army Signal Corps equipment collections
- military meteorological instrument displays
- Plotting Board ML-55 restoration or completion projects
- field artillery weather-support reference collections
- museum exhibits on military weather observation
- collectors of ML-series Signal Corps equipment
- military plotting, drafting, and protractor accessory collections
- archive and research displays focused on technical support equipment
This listing is for the Scale ML-137 only unless otherwise stated. No Plotting Board ML-55, theodolite, balloon equipment, case, manual, forms, or additional accessories are included unless specifically shown or noted.
Why This Scale Matters
Many military collectibles focus on weapons, vehicles, uniforms, helmets, or manuals. This item documents a different but equally important subject: the technical equipment used to support military weather observation and wind-data plotting.
For collectors, it is a focused Signal Corps accessory with a direct connection to Plotting Board ML-55 and ML-series meteorological equipment. For researchers, it provides a useful reference point for how field weather data was plotted and interpreted before modern digital systems. For museums, it helps explain the behind-the-scenes equipment that supported artillery, balloon observation, meteorological sections, and technical field operations.
Because small accessories like this were often separated from their original plotting boards, surviving examples are valued not only for their physical form, but also for their connection to complete military meteorological equipment sets.
Ideal For
This scale is a strong fit for:
- Signal Corps meteorological equipment collectors
- Plotting Board ML-55 display and restoration projects
- field artillery meteorological support collections
- World War II and early Cold War technical equipment displays
- military weather-service and pilot-balloon observation collections
- collectors of military plotting scales, protractors, and technical accessories
- buyers looking for a specialized Scale ML-137 for ML-series equipment displays
Approx length 11.5", Approx width 5.5", Approx height .1", Approx weight .2lbs.
Pictures are stock images of our inventory. Unless otherwise noted, you will not be receiving the exact item shown in the pictures. The pictures are representative of the item's general condition. The item you receive might be slightly better, or worse, condition than was shown in the pictures.
Please visit our page about order lead times here: Order Lead Times