By: Matt_D

Matt_D — Tue, 19 Nov 2013 20:34:35 +0000

The CED M2’s processor has a clock speed of 48 MHz. Which makes its error rate per clock cycle (given a 3000 fps bullet) 0.0125% (0.375 fps), not 0.6%.

The Shooting Chrony chronographs all have a 1 MHz processor, the slowest of any chrono on the market. And if you’ll bother to dig in and read their documentation, you’ll find that the 0.5% error rate they advertise is with a 2000 fps bullet. Which extrapolates to 0.75% at 3000 fps, at which velocity the average error would be 22.5 fps. So good luck with your dreams of hand loading to a single-digit SD when your chrono randomly introduces 20+ fps errors.

If a Shooting Chrony is a bargain worth the money, then I suppose you could say the same for the Ford Pinto. That you are satisfied with yours only can mean either your requirements or your standards are very, very low.

By: Josh Benin

Josh Benin — Sat, 21 Apr 2007 17:51:18 +0000

I read with much interest your recent blog article on the new CED ‘M2′ Chhronograph, and the included comments on chronograph accuracy – interesting because chronographs are the one handloaders’ tool which we cannot check. I encourage you to complete the comparative test between chronographs you mentioned. While it won’t be conclusive, it certainly should be interesting.
A couple of comments on your concern with the extreme spreads from your Shooting Chrony are appropriate. If a chronograph uses a 1 foot screen spacing (common among lower-cost models), and a 1 mHz clock (this is a guess), a 3000 fps projectile takes 1/3000 of a second to cross the screens, the clock counts 333 cycles, and a +/- 1 count error will be 2/333 or 0.6%. This equates to 18 fps and compares with the 0.5% error Shooting Chrony claims in their website. On this basis alone, you should not be especially concerned with the ES values of 30-50 fps you mentioned. They are reasonable compared with instrumental accuracy. If you want better data, drill the pivot rivets out of your Shooting Chrony, lengthen the cable, and increase the screen spacing to 5 or 10 feet for a low-cost accuracy improvement of 5 to 10X.
Better yet, forget about ES altogether – statisticians have already solved the problem. The standard deviation, while not intuitive, is exactly what you want, and given a sufficient sample, will not be affected by measurement errors described above. Your chronograph probably already calculates the SD for you. Use it. Chances are, 95% of your shots will be within 2 SD of the average, or chances are 1 shot in 20 won’t be.
No, I have no association with Shooting Chrony, although I do own one and think that for $55 it was a great bargain. Understand that it’s a tool for the casual user, not a lab instrument, its limitations are exactly as you’ve described, and the work-around is either lengthen the spacing, or just forget ES and use the SD.

Comments on: New CED 'M2' Chronograph

By: Matt_D

By: Josh Benin