Casio BM-100 – Technical Data & Model Information

Casio BM-100 is a digital outdoor watch released around 1989. It used module 560 and introduced Casio’s first pressure-sensor system, combining a barometer, trend graph, altimeter, and a rare depth meter in one compact resin case. Collectors see it as the “zero-generation” model that started the entire Casio BM barometer family.

In later years this watch led directly to the rest of the BM line. The BM-200 continued the idea with a new design and a focus on trekking functions such as ascent/descent speed. The BM-500 followed a different path by keeping the full sensor set (including the depth meter) and using an analog-digital dial style. In the mid-90s the BM-600 / BM-610 refined the concept again with a more ProTrek-like look and barometer + altimeter functions without the depth meter.

Casio BM-100 – Quick Technical Data

Field	Data
Model	Casio BM-100
Module	560 (early units also documented with module 510)
Battery	2× SR927SW (equivalent to 395)
Manual	Casio BM-100 Manual
Glass Type	Probably mineral glass
Strap Size	18 mm lug width / 23–24 mm case connection
Case Material	Resin case, front-mounted pressure sensor grill, Japan-made
Functions	Barometer, pressure-trend graph, altimeter, depth meter, timer, stopwatch, alarms, hourly signal, LED light
Production Years	Around 1989–1990, documented as BM-100WJ (February 1989)

What color versions of Casio BM-100 exist?

The Casio BM-100 came in five known color variants. All versions share the same module and sensor system, but the colors and small details make a big difference for collectors. Below is the list from the most common to the very rare pieces.

1. BM-100 Black Version (most common)

• Full black case and strap.
• Black sensor grill and white “DIGITAL BAROMETER” text.
• This is the version most people remember and the one that appears most often for sale.

2. BM-100 Black with Yellow Buttons

• Same black case and strap as the standard model.
• Yellow side buttons add a sporty look and make the watch stand out.
• Noticeably rarer than the full black version.

3. BM-100 Black with Yellow Front Grill

• Black case and strap.
• Yellow grill plate on the front, fixed with silver screws.
• Gives the watch a more industrial, “tool-like” style.
• Harder to find in good condition because the grill often fades.

4. BM-100 Green with Yellow Grill (very rare)

• Green case and strap.
• Yellow grill on the front, similar to the black/yellow version.
• Produced in smaller numbers, highly desirable among outdoor Casio collectors.

5. BM-100 Full Green Version (very rare)

• Dark green case and strap.
• Black grill on the front.
• The rarest BM-100 variation. Only a handful of photos are known online.

Rarity ranking (common → rare)

Black → Black + yellow buttons → Black + yellow grill → Full green = Green + yellow grill

About the Casio BM-100 sensor system

The Casio BM-100 uses an early semiconductor pressure sensor mounted behind the front grill. This small component is the heart of the watch. It measures atmospheric pressure every few hours and turns the data into a simple vertical graph on the right side of the display. The same sensor also powers the altimeter and the depth meter, which makes the BM-100 unique among late-80s Casio models.

Barometer and weather trend

• The sensor reads air pressure in millibars.
• The graph updates roughly every 1–3 hours.
• Rising bars usually mean improving weather.
• Falling bars indicate clouds and possible rain.

Collectors like this feature because it works even today if the sensor is healthy.

Altimeter

• Uses the same pressure sensor to estimate height above sea level.
• Shows higher numbers when you ascend and lower when you descend.
• It is a simple altitude reading, not GPS-based.

Depth meter

• A very rare feature in Casio watches.
• Measures depth below sea level using pressure changes.
• This makes the BM-100 a “mini weather station + depth tool” in one watch.

Sensor quirks

• After a battery change the graph resets and needs about a day to collect new pressure data.
• A damaged sensor cannot be replaced with modern parts. Only a donor BM-100 sensor works.
• Sensors from BM-610 look similar but are not compatible.

More technical details

A collector documented a full sensor replacement, including photos, calibration notes and comments from Fujikura (the sensor manufacturer). It is one of the best technical resources for this model: https://www.watchuseek.com/threads/back-from-the-grave-casio-bm-100wj-long-post.450442/

Production years and model background

The Casio BM-100 appeared around 1989–1990, with the best-documented version being the BM-100WJ from February 1989. It was sold in Japan and overseas (BM-100J for the US market) and quickly became known as one of Casio’s most advanced digital tools of the late 80s. Collectors sometimes call it the “proto-ABC” because it already offered altitude, barometer, and depth functions long before the modern triple-sensor line.

The watch is Japan-made and uses either module 560 or the earlier module 510. Both versions look the same to users. The pressure sensor sits behind a metal grill on the front of the case and logs pressure every few hours to build the trend graph. This simple system became the base for all later BM models.

Over the next years the BM-100 inspired the whole family:

• The BM-200 continued the idea with a trekking-oriented design and ascent/descent speed.
• The BM-500 kept the full sensor set and used an analog-digital display.
• The BM-600 / BM-610 moved closer to the early ProTrek style with a large graphic screen.

Collectors today see the BM-100 as the watch that started it all: a small resin “weather station” that shows how Casio experimented with sensors before the outdoor line fully evolved.

Collector Notes

The Casio BM-100 is most common in its full-black version, while the yellow-accent and especially the two green variants are much harder to find. Collectors pay close attention to the front grill because the printed text fades easily, and a sharp, clean grill usually means a well-preserved watch. The sensor is the critical component: it controls the barometer, altimeter and depth meter, and it cannot be replaced with modern parts. Only a donor BM-100 works because each sensor was individually calibrated to its module.

Original straps are difficult to source, although NOS pieces still appear occasionally. A BM-500 strap can be adapted, but it needs trimming to 18 mm at the lugs. Inside the case, the small circular gasket under the sensor is important for long-term reliability, and collectors often re-grease it with silicone. After battery changes the watch may show “FULL” or “ERROR”, so an AC reset and checking the tiny sensor springs is usually enough. Good-condition BM-100 units with a healthy sensor remain highly collectible and a key piece of Casio sensor history.

Other BM watches and model evolution

The Casio BM-100 is the first watch in the BM barometer family. All later BM models build on the same idea: a pressure sensor that shows weather trends and altitude changes. Each generation moved the concept in a slightly different direction.

The BM-200 is the closest successor. It keeps the barometer and altimeter but removes the depth meter and adds ascent/descent speed, making it more of a trekking tool. The design also changed to the famous “mask-style” front.

The BM-500 develops a parallel path. It keeps the full sensor set of the BM-100, including the depth meter, but switches to an analog–digital display with colored scales. It feels more like a technical instrument and is often praised for its usability.

The final evolution appears in the BM-600. These models drop the depth function and focus on altitude + barometer, with a new oval display that looks close to early ProTrek watches. They are the “bridge” between the BM line and the later outdoor series.

For collectors, the BM-100 remains the foundation. The BM-200 and BM-600 continue the trekking-focused direction, while the BM-500 preserves the full sensor spirit of the original.

FAQ – Casio BM-100