Version Three
If you are not sure which version cb625 you have click here to get back to the page that helps you too decide.

Start with the basics. You turn it on by pressing and releasing the RST button. It then shows READY and waits for a pellet to be fired through its sensors. If you do nothing after 60 seconds it will turn itself off automatically. If you want to turn it off before that press RST and hold it down. First the display shows all the segments on for about a second and a half then the display goes blank. Release the RST button now and it is switched off. The picture above is a virtual chronoscope. Click the RST button and watch. Then Click and hold it and see what happens.

Before firing the gun be sure to align the cb625 correctly and securely on the barrel. The pellet must fly through the centre of both rings on the top of the unit. The beam of infrared light is about the diameter of a cocktail stick so adjust the height of the mount carefully and attach securely. Shooting a hole in the device does not constitute a warranty repair. If you have a break barrel gun with significant recoil be warned that if the gun kicks it can cause the cb625 to move into the pellet path if it is not secured.

Pressing and quickly the RST button places the cb625 in READY mode. This means that the infrared lights and sensors are switched on and it is waiting for a pellet. Always check the display at this moment.

Imperial mode
ft/sec and ft-lbs

Metric mode
meters/sec and joules

Once a pellet has been detected by the first sensor the cb625 starts its timer going and waits for the second sensor to report. The counts are made at four millionth a second as the pellet travels the 2.346 inches. If the second sensor does not report a pellet, perhaps the chronoscope was not on straight, the display shows bAd. You can emulate this by selecting the Bad button next to the pellet. The Fast button sends a pellet at about 900ft/sec and the Slow button at about 250 ft/sec.
If all goes well the second sensor sees the pellet and calculates the velocity in feet per second. It then uses the pellet weight to calculate the actual power and then displays one of them. If you press the FPS button you see the speed and if you press the PDS button you see power. The cb625 remembers which you selected last and returns to that display after a new shot is fired. If the power is below the power set as the legal limit the display shows LEGAL. Otherwise it shows FAC.

Group of shots. If you continue to hold down either the FPS or the PDS buttons the cb625 changes the display to show in turn the average, the minimum and finally the maximum of the value selected. To clear the averaging buffers to start a new group hold down both FPS and PDS until the display shows 000. Press RST to continue.

Hold down the RST button and the cb625 cycles through its configuration options. Release RST at the item you require.
Display all on This is a simple test to ensure that all segments of the display are operational.
Display off. If you release RST now it switches off. You can use this to save having to wait for the unit to time out.
Pellet weight. As power depends on weight the chronoscope needs to know the weight in grains of the pellet. It starts with a default value of 15.0 grains. What happens is that the digit on the right begins to flash. If you press the PDS button again the flash moves to the middle digit and again to the right hand one and then back to the left hand side. Each time you press the FPS button the flashing digit increases by one until it makes 9 when it goes back to 0 so you can set any pellet weight up to 99.9 grains. When you are happy press RST and the value is saved.
Please note that changing the pellet weight does not act retrospectively. The memory of the power of the last shot is still recorded as it was calculated with the old weight.
Gb/Eur. This changes the mode between the old Imperial system working in speeds in feet per second, weights in grains and power in foot pounds and the Metric system with speeds in meters per second, weights in grams and power in Joules. Use the FPS button to switch back and forth and press RST when the display shows the one you want.
Adjusting the legal limit. This works much the same as the weight. Use PDS to select the digit and FPS to increment that digit. In the UK the limit for rifles is 12.0 ft-lbs and for a pistol it is 6.0 ft-lbs. When you have the correct limit shown press RST.

Calibration settings. The cb625 should provide accuracy to within 1% if used properly however some people prefer to be able to fine tune it to match another chronoscope. The calibration value is normally set to 100 but by adjusting it down to zero you can make the cb625 read 1% slow and by adjusting it to 199 you can make it read 1% fast with other values in step.
Serial link testing. The display reads Snd and pressing FPS simulates a 280fps shot and pressing PDS simulates 810fps.

The serial output. The little three pin connector near the clamp bolt allows you to connect your cb-625 directly to a computer. See elsewhere on this web-site for details of the interface to buy or here for the details to build one. In brief the output is 9600 baud, 8 bit ASCII, no parity, one stop bit as 0-5 volts that needs inverting and converting to the RS232 for the computer. The output is an ASCII text number followed by representing the number of 4MHz counts to cover the 2.353 inch gap so "1000" represents 784ft/sec. There is free software available on this site for Windows systems to collect and display this data.

What goes wrong?
A blocked sensor: dirt or damage can block the beam of infra-red light used to detect the pellet. If you look into the rings on the top of the chronoscope you will see a little round thing on both sides. It is nestled down into the plastic to try and protect it but a beam of light is projected from one side to the other while the chronoscope is in READY mode. If either sensor is inoperable it displays the sun-behind-clouds logo on the display when you press RST and refuse to got to READY. If you are not getting readings inspect the sensors. If your gun is oily they could be fouled. If they are damaged do not abandon hope. In the UK Combro offer a quick and inexpensive repair service.
Flat batteries: The highest demand for power from the batteries is when the system goes to READY with its lights on. If the display goes dim then it is too late. In the UK Combro stock batteries at a low cost because if you buy them from a chemist they are rather expensive.
You can power the cb625 from an external 6 volt supply through the 3 pin connector. The centre pin must be the negative terminal and both the outer pins the positive. When you connect power this way the cb625 detects it and goes into alto-ready mode. This means that after you fire a shot and it displays the results the ready indicator comes back on and you can fire another shot. This is why the Combro computer interface adapter has a container for four AA cells as if you power the cb625 like that you can fire many shots and they will all be logged by the computer.

If you get stuck ring - In the UK Combro are at 01323-899950