Casio 3731 Operation Manual Download Page 2

Operation Guide 3731

2

The power supply of this watch uses a solar cell to generate
electrical power, which is stored by a rechargeable battery. Using
or storing the watch where it is not regularly exposed to light, or
allowing it to be blocked from light by your sleeve for long periods
as you are wearing it can cause the power of the rechargeable
battery to run down. To ensure stable operation, be sure to allow
the watch to be exposed to light as much as possible when you
are wearing or storing it.

Note that all data in memory and all settings are cleared
whenever you allow the level of the rechargeable battery
to drop to Level 4.

Battery Level Indicator

Level 2

Level 3

Level 4

Level 1

Normal operation 
enabled.

Digital display, illumination, 
alarms, tones (alarms, 
hourly time signal), signal 
reception, digital-analog 
synchronization disabled. 

All functions, including 
timekeeping, disabled.

Normal operation 
enabled.

In the Stopwatch Mode, the battery level indicator dial functions
as the elapsed time minute hand.

Exposing the watch to direct sunlight or other strong light may
cause the battery level indicator to indicate a level momentarily
that is higher than the actual battery level. Because of this, you
should wait for a short while after charging to check the battery
level indicator.

Signal reception resumes when the battery is recharged to Level
2.

Even after the battery drops to Level 4, you will be able to resume
normal operation by charging the battery. After the digital display
appears, configure time and date settings.

Start charging at Level 3!

Battery Level 3 indicates that remaining battery power is very low.
Be sure to expose the watch to light for recharging as soon as
possible after Level 3 is indicated.

Flashing Recover Indicator

If you use the light or alarm a number of times during a short
period, a recover (R) indicator flashes on the display and the
following operations become disabled as battery power recovers.

Display illumination,

Alarm and hourly time signal

Time calibration signal reception

Analog-digital synchronization

Normal operation will return after the
battery recovers.

Recover Indicator

Charging Guide

Starting from a full charge, the watch
should be able to continue operating
for about five months without further
charging under the conditions
described below.

Daily Use (All time values are
approximate.)

Illumination: 1.5 seconds

Alarm: 10 seconds

Signal reception: 5 times

Making sure the watch is regularly
exposed to light ensures stable
operation.

Charge Times Required to Advance to a Higher Level

Approximate Exposure Time

Level 4  

\

 Level 3  

\

 Level 2  

\

 Level 1 

– – –

– – –

– – –

– – –

1 hours

4 hours

14 hours

3 hours

5 hours

49 hours

20 hours

71 hours

Exposure Level 

(Brightness)

Outdoor Sunlight 

(50,000 lux)

Daylight Through a Window on 

an Overcast Day (5,000 lux)

Indoor Fluorescent 

Lighting (500 lux)

Sunlight Through a 

Window (10,000 lux)

Note that the above charging times are for reference only. Actual
charging time depends on a variety of environmental factors.

Required Daily Charging Time 

• 

The following is the daily 
amount of charging required 
each day to support the 
operations under “Daily Use”.

Exposure Level 

(Brightness)

Outdoor Sunlight 

(50,000 lux)

5 minutes

24 minutes

48 minutes

8 hours 

Sunlight Through 

a Window 

(10,000 lux)

Daylight Through a 

Window on an Overcast 

Day (5,000 lux)

Indoor 

Fluorescent 

Lighting (500 lux)

Approximate 

Exposure 

Time

Power Supply

An LED light is used to illuminate the face of the watch for easy
reading in the dark. An auto light switch automatically illuminates
the face when you angle the watch towards your eyes for reading.

To illuminate the face manually

Press the 

D

D

D

D

D

 button in any

mode (as long as a setting
screen is not displayed) to
illuminate the face of the
watch.

Pressing the 

D

 button illuminates the face regardless of whether

the auto light switch is on or off.

You can use the procedure under “To specify the illumination
duration” to configure the illumination duration as approximately
1.5 seconds or 2 seconds.

You may hear a faint rattling sound when you move the watch
around. This sound is caused by the movement of a metal
bulb that controls operation of the auto light switch, and does
not indicate malfunction.

To illuminate the face with the auto light
switch

The auto light switch automatically illuminates the face
whenever you angle the watch towards your eyes for reading,
but only when it is dark.

The auto light switch does not illuminate the face when
surrounding light is bright.

You can use the procedure under “To specify the illumination
duration” to configure the illumination duration as
approximately 1.5 seconds or 2 seconds.

To turn the auto light switch on and off

While any screen (besides a flashing setting screen) is on the
display, hold down the 

D

 button for about two seconds to toggle

the auto light switch on (auto light switch on indicator displayed)
and off (no indicator displayed).

Auto Light Switch 
On Indicator

(Light)

Positioning Your Arm Correctly

1

2

With the watch on 
your wrist, position it 
level with the ground.

Rotate your arm so the watch 
is angled at about 40 degrees, 
so you can read its face.

At least 
40 
degrees

You should be wearing the watch on the outside of your wrist
when using the auto light switch.

Make sure that the left (9 o’clock) and
right (3 o’clock) sides of the watch are
within 

±

15 degrees of being parallel

with the ground. The auto light switch
may not operate properly if the angle is
greater.

Important!

The light may be difficult to see if you turn it on under bright
sunlight.

If you press any button or if an alarm operation starts while the
face is illuminated, illumination will turn off.

Auto Light Precautions

Frequent use of the auto light can run down the battery.

The auto light switch may cause the face to illuminate when your
sleeve covers the face of the watch.

The face may not illuminate immediately when you angle the
watch towards your face. This does not indicate malfunction.

The face remains illuminated for the currently set duration (1.5 or
2 seconds) only, even if you leave the watch angled towards your
face.

The face may illuminate unintentionally when you wear the watch
on the inside of your wrist, when you shake your arm, or when
you raise your arm. Be sure to turn off the auto light switch
whenever you do not need face illumination
.

Keep the auto light switch turned off whenever you are wearing
the watch on the inside of your wrist.

Electro-static charge and magnetism can interfere with auto light
operation and even make operation impossible. If this happens
lower your arm to the starting position and then raise it again. If
you still have trouble with illumination, try lowering your arm down
to your side and then raise it to your face for reading.

Face Illumination

Charging Precautions

Avoid charging the watch in the following locations, and anywhere
else where the watch may become very hot.

On the dashboard of an automobile parked in the sun

Very close to an incandescent light source or other sources of
heat

In a location exposed to direct sunlight for long periods or a
location that is very hot

Note that the display panel may become black under very high
temperatures. This is temporary, and the display will appear
normal again at lower temperatures.

Depending on the light source you are using, the
case of the watch may become quite hot during
charging. Take care to guard against burn injury
after charging.

To charge the battery

Point the solar panel (face) of the watch at a light source.

Remember that even a partial blockage of the solar cell reduces
charging efficiency.

Example: Positioning the watch

Solar Cell

The illustration shows the resin band model.

Summary of Contents for 3731

Page 1: ...Hands move to 12 o clock Moves to current level Returns to current seconds position Time in Current Time Zone Time Zone TIME DIFFERENCE Alarm Number Alarm Time How the sleep state works Display sleep state The display sleep state is triggered whenever the watch is left in the dark for three or four days The display goes blank in the display sleep state Alarms and the hourly time signal continue to...

Page 2: ...the face of the watch Pressing the D button illuminates the face regardless of whether the auto light switch is on or off You can use the procedure under To specify the illumination duration to configure the illumination duration as approximately 1 5 seconds or 2 seconds You may hear a faint rattling sound when you move the watch around This sound is caused by the movement of a metal bulb that con...

Page 3: ...onfigured to select the strongest Japanese signal 40kHz Mt Otakadoya signal or 60kHz Mt Hagane signal and use that one for calibration is stronger 1000km Mt Hagane 60kHz Mt Otakadoya 40kHz 500km 1000km 500km Japan Transmitter Locations Under optimum conditions the calibration signal should be receivable up to 1 000 kilometers from the transmitter Note that the wave is relatively weak at distances ...

Page 4: ...s will cause the watch to beep and then exit the receive operation Make sure you are within the range of the calibration signal transmitter before performing the reception operation Remember that geographic contours nearby buildings seasonal conditions the time of day can even make reception impossible even when you are within range of the transmitter Proper reception may be impossible if there is...

Page 5: ...ute setting flashes Hour Forward Back Minute 5 Use the D D D D D and B B B B B buttons to change the minute setting Holding down either button scrolls the setting at high speed 6 When the setting is the way you want press the A A A A A button This exits the setting screen An alarm is turned on automatically whenever you change its settings The display also will exit the setting screen automaticall...

Page 6: ...ime Though the digital time freezes the stopwatch hands continue to move This stops the elapsed time operation Pressing the A button while timing is stopped resets the stopwatch Resetting the stopwatch stores the final elapsed time that is on the display to lap split time memory Start Lap Number Lap Lap Time Reset Stop Start Split Split Time Reset Stop Lap Time Display Split Time Display Elapsed T...

Page 7: ...ing the A button in the Dual Time Mode displays the time differential of the currently selected time zone for about one second Time Zone Time in selected time zone Forward Using Summer Time DST Summer time or Daylight Saving Time DST as it is called in some countries calls for setting clocks ahead one hour during the summer season Note that the use of summer time depends on the country and even th...

Page 8: ... D D D D D button to reset them to 00 in accordance with the time signal on the radio TV etc Pressing the D button while the seconds count is in the range of 30 to 59 resets it to 00 and also adds 1 to the minutes Pressing the D button in the range of 00 to 29 resets the seconds count without changing the minutes 9 While the hour minutes year month or day setting is flashing use the D D D D D butt...

Page 9: ...il it completes a 12 hour cycle or until you press any button to stop it 6 Press the A A A A A button to select the stopwatch 1 20 second hand for adjustment 24 hour hand Minute Hand Hour Hand Forward Back 7 If the 1 20 second hand is not aligned with the 12 o clock position use the D D D D D button to adjust it Each press of the D button advances the 1 20 second hand by one step Holding down the ...

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