Last updated 2007.12.27

Can the Combro cb625 replace my regular chronoscope for other pistols and rifles?
No. The cb625 is designed specifically for airguns of .177 and .22 calibres only. Using any other firearms on it will cause extensive damage to the chronoscope AND YOURSELF!
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What is the computer interface for?
Note:Combro si-625 interface is no longer in production. Following information is for current users or those who acquired them through used item markets.

The computer interface allows you to use the cb625 in a more efficient way. Instead of a small window displaying, in turn, the velocity and energy level of the shot just fired, the interface displays on the computer screen up to three windows.

The first window lets you configure the software to your specifications such as which COM port to use, whether you want the log file, and several choices of .WAV files for sound effects. This window also shows the velocity and energy level ( you have to enter the pellet weight for calculation ) of the last shot, the average velocity and energy so far, and the number of shots recorded.

If you click BIG on the manu bar, a big window ( re-sizable ) showing the velocity and energy of the last shot appears, with the numbers in an eye-catching red.

Click on AVERAGES | ADVANCED STATISTICS ON/OFF and a third window pops up. It updates the statistics as each shot is fired, showing, for both velocity and energy, maximum, minimum, average, range, and finally the RMS ( 'root mean square', also known as 'standard deviation, SD' ) for those who are mathematically inclined.
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What is RMS?
"RMS" stands for "Root Mean Square". It is a measure of how much spread there is in the values. It is also known as the standard deviation and no statistician would be without one. In essence it is the plus/minus range that we would expect 62% of the shots to come within.

If your adjustments make this figure smaller you are improving the consistency of the gun and it becomes more predictable. If this figure become larger then your gun is less consistent and hence the effects of range and windage are less possible to predict.
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How do I mount the combro-625 to my air pistol? I had no problems with my air rifle.
The combro-625 was originally designed for rifle barrels, so you will need to modify the unit a little to make it center with the barrel of an air pistol, which usually have the cylinder right beneath the barrel. Following is what I did to make it fit my air pistols:

If you look down the front part of the V-block you will see the T-ridge which slides into the groove on the back of the 625. This T-ridge is too short for use in air pistols. So the main idea is to extend this T-ridge up high enough to go into the groove on the unit.

I cut off a section of wire from a coat-hanger ( the kind you get from dry cleaners ) and bend it into a very narrow inverted U, and slide it upwards into the grove on the 625 to make it fit. Adjust the width of the U so it fits snuggly into the groove. This is the extension of the T-ridge, and it should be about 2.5 to 3 cm, depending on the cylinder and barrel configuration of your pistol. If it is too long it will get in the way of the barrel and get hit by the pellet. If it is too short the extension will not be sufficient to allow the 625 to center with the barrel axis. So there is a bit of trial and error.

Once you determined the length of this section you can bend the two legs of the inverted U outwards a little, and then straight down again. This is to widen the U to allow the lower section to fit over the V-block right behind the T-ridge. You can then bend the end of the wire back up right behind the two legs you just made. Once that is all done, you can use a piece of rubber band to secure this extension to the V-block.

You do not have to remove this set up unless you are going back to a rifle. But once the wire part is made up, taking it off and putting it back on is only a matter of seconds.

Please see following sketches:

I find it difficult to align the combro properly. Any tricks to it?
Mount the Combro on your airgun first. Then, before you turn on the power, carefully insert a long rod through the Combro's sensors and into the barrel. You can use a cleaning rod, a knitting needle ( preferably plastic ), or similar items. It should be long enough to stay inside the barrel and pass through both sensors on the Combro, and it should be thick enough to stay put and not wobble.

Use this rod to aid you in making adjustments. View from the side as well as from the top, and move the combro till you are satisfied that the rod is running through the middle of both sensors.

Now turn on the power. You should see a cloud icon on the top of the display, and a wide '|---|' in the main display. This indicates both the first and the second sensors are blocked. Of course they are, because of the rod you put in. This also means that you have correctly aligned the sensors. Since the pellet coming out from the muzzle should be flying at almost a straight line, the rod is a simulated way to block the sensors in place of the pellet.

If you see '|---' or '---|' then only one sensor is blocked, and you should readjust the Combro's position.

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