Which Chronograph? **UPDATE**

Over the years I have owned or used numerous models of chronographs. I have found that if used as instructed and if properly calibrated they are all decent. Currently I have 2 types one is a Chrony beta master which is the Chrony top of the line it has all the bells and whistles and it comes with a printer. Lately I have been using a small unit that attaches to the barrel that was made for air rifles it’s a Combro CB-625 mk IV I found it on eBay it comes from England it was realitivly inexpensive ($85) what I like best it only takes 10 seconds to attach and its extremely convenient no sun shield needed no tripod it can fit in a shirt pocket. Frankly using a Crono was a pain in the ass necessity when fine tuning my air rifles by using the Combro I can quickly check my rifles performance and immediately make the proper adjustments.
this is were I got it took about 10 days to arrive.
https://www.ebay.com/itm/COMBRO-CB-625-Mk4-Air-Rifle-Gun-Chronograph-Chronoscope-Ft-lbs-Shooting-Aligner/331701266190?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

https://youtu.be/KRwPmEDB8dI

i still use the standard unit when I’m not lazy. 
Idid have the Caldwell unit your considering it worked well . I have found that that once you figure out where in the inverted triangle (mine was half way up and only an inch or so height sweet spot) you must place the projectile it works fine
 
I use the caldwell with the light kit and never get an error unless I screw up and am not shooting over both sensors. Works extremely well and for a good price. The prochrono digital chronograph works excellent also and gives you all the info like ES, SD and saves your whole shot string on the chrono itself. Caldwell does the same but you have to connect it to a tablet or smartphone.

No matter what chrono you buy, GET A LIGHT KIT!!! It will save you many headaches. :)
 
No one ask, but here is my two cents.

The upside-down Caldwell seems to work better under low light conditions than any of the Chrony series (at least compared to my Alpha Chrony). I do have a light kit for the latter, but it isn't much help in my opinion.

I have a small Listone L1000 that works well, but the pass through is only 2 inches square limiting its use (and appeal).

Forget the Magnetospeed standard model as it won't work with airguns. It takes the V3 model to do that, and at about $375 for muzzle-only FPS, it is a bit pricy. And don't expect any accuracy at all with it attached. 

I first borrowed a Labradar, but just could not get the thing to work as advertised. With some assurance that a new one would work, I bought one. It works very well for .25 caliber and larger airguns, but falls a bit short (lots of errors—no readings) for .22 and .177 calibers. It sees my .25 caliber out to about 75 yards, and my 9 mm out to about 125 yards, under low wind conditions. The drawback is the cost. With microphone extension kit (required for airguns), carrying case, bench mount or tripod, it is close to $700 delivered. This is offset a bit as you can easily calculate the BC with the data supplied by the Labradar (velocity at a number of distances). Is it worth the monies? Yes, if you do a lot of tuning for yourself, or as a group buy for a club. Otherwise, the Caldwell is on the tp of the heap.

 
Davemac18,
the Combro device can be mounted on the bottom, either side or on top of barrel. On some of my guns the pcp air tank extends to the barrel end and I then attach on the side or to a screw on moderator. Remember it is held on with rubber bands which are flexible enough to go around the sight. On offset barrels they ae best on bottom or top the side doesn't work. I've only used it on air rifles I'm not sure if it would work on high power powder burners. The best thing about it is a 30 second or less job to set up were i find the others though they work they are a PITA.
 
I've been using the Caldwell deluxe chronograph with IR lights and plug-in access for the readouts with Android app. Even with the wall wort plugged in for the lights, I still get runs of ERROR2 and ERROR3? Other times, it does that, and gives numbers like 13, 856 or the like? After seemingly warming up, it'll then work flawlessly. I think it's loosing it's mini-mind...