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Geiger Counter Watch and Much More!!!!!  You just gotta have one!!!

Last December, our labs acquired a Gamma Master watch from Latitude Limited out of Hong Kong.  Our purpose was to determine how effective this type of radiation detector would be in real working situations. This was the best decision we have made in a long time. Not only did the watch live up to its publicity, we had a great time testing (playing with) it over the past few months.  This watch is a must-have for all radiation professionals.

There is no substitute for the radiation professional being able to know his accumulated Dose Equivalent or the background readings at all times. It gives the professional a live sense of the radiation environment never truly known before.

With the new emphasis on radiation terrorism, we recommend this watch for use to detect dirty weapons by anyone concerned - police – customs – firemen – etc... etc. .

During our evaluation of the watch we used it all over the world. It never deviated from being consistent with larger instruments for detecting background radiation through fairly high levels during our work and during training courses. We compared its readings over the test period with a Victoreen Scintillation Counter Model 190/429. It stayed within 5% of the readings we had using the Victoreen Instrument. Considering the watch case  next to the technicians wrist versus the probe of the Victoreen extended away from the body… we were impressed.

Not only could we use the watch as our radiation detector, it gave us a running account of accumulated Dose plus background level changes. The background of our labs ranged from 0.09 mSv/hr to 0.35 mSv/hr.  The average was approximately 0.13 mSv/hr.  It is truly a joy to be able to see bursts in background due to sun spot activity or other unknown sources. 

When we were doing radiation surveys, we could add a feature to our reports: background level changes. The Gamma Master is amazing to be so sensitive to allow such a report.  Most of us who do surveys only write down the “hot” spots.  With the Gamma Master  the professional is able to determine real time changes to the background in the area making this a true ALARA Tool.

During our travels, we took many airplane trips with the Gamma Master. What a professionally interesting gadget is this watch that allows us to see the increases in our radiation exposure as the airplane climbs through the atmosphere. The following table is one we use during our training sessions on Radiation Safety. The Gamma Master  followed this table at least as high as we traveled in normal commercial jetliners.  We saw a high of 6.00 mSv/hr at approximately 35,000 feet several times across the USA and to Europe. Typically the Dose Rate was approximately 3.5 mSv/hr for most trips.  We saw very little changes during the first 15,000 feet of climb but afterwards the background rapidly changed as the airplane reached cruising altitudes.


Average Annual Dose (mSv)

Average Dose Rate (mSv/hr)

Sea Level

















When we went through airport security we had to place the watch on a separate carrier as we did our cell phone and laptop computer. Each time the watch came through the X-ray machine fine. It was alarming its heart out but functioned beautifully... that is all times except one. Dallas Fort Worth Airport Delta check-in blew our beautiful Gamma Master. We believe the X-ray machine was set a "little high." I wonder how the leakage is for the workers there? With the new security arrangements, one may not ask such questions at the check point without the possibility of being labeled a "problem."

We sent our Gamma Master back to Latitude for repair. It was returned very quickly.

Take our word for it. This is a necessary piece of equipment for all radiation professionals. Get One.


The Gamma Master has four distinct displays:  The analog watch face, a graphic display of Dose Equivalent Rate, a graphic display of Accumulated Dose Equivalent  and a digital readout which may be switched between Dose Equivalent Rate, Accumulated Dose Equivalent and time.

The following are the features on the watch’s data sheet.

Detecting Gamma-radiation with Geiger-Muller tube
Measurement of Dose Equivalent Rate (DER) and Dose Equivalents (DE) of Gamma-radiation
Graphical and digital indications for DER and DE
User set DER and DE audible alarms
Digital watch displays hour and minute, date and second
Daily alarm

Analog watch indicates hour, minute and second
Electro-luminescent back light
Metal case, metal band and switch buckle

DER indication range: 0.1 to 4000mSv/h (0.01;0.1;1.0;10.0;100)
DE indication range: 0.0001 to 9999mSv
DE threshold range (step): 0.001 to 9999 mSv (0.001; 0.01; 0.1;1.0;10.0;100)
DE accumulation time range: 1 to 9999 h
Accuracy of indication of DE:+/- 25%
Energy range: 0.06 to 1.5 MeV
Measurement time decreases automatically in the range: 300 to 2 s

Latitude Limited
Health-care Watch Series
11/F., Hoi Hung Industrial Building
25-27 Lam Tin St
Kwai Chung
N.T. Hong Kong
Tel:  (852) 2410 0338
Fax:  (852) 2494 0993