# Cosine/angle

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by robbor, Jun 11, 2007.

1. ### robborWell-Known Member

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Im building a cosine angle indicator and am wondering how many significant digits I should use for long range. I notice that the ACI only uses 2 digits and I just captured a pic from the back of a Suunto angle indicator and they use 4 digits. Any body play with more than 2 digits for long range?

5degrees off of level: ACI .99 Suunto .9962
15 .96 .9659
25 .91 .9063

Looks like they only differ by about 4 yards or so out to 1000.

2. ### MikecrWell-Known Member

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Also, why not just drop the whole 'cosine angle' business. It's angle, in degrees, from an inclinometer. If digital and 4 places, fine, but not necescary.

3. ### CatShooterWell-Known Member

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Two digits is more than enough.

4. ### BuffalobobWriters Guild

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Robbor

Most scopes are graduated in 0.25 inches or MOA as the case may be.

At 1000 yards 0.25 MOA is about 2.5 inches at 2000 yards it is about 5 inches. If all other things are correct then by being off 0.125MOA one would still be very well within the kill zone of any reasonable target, military or hunting. So your angle indicator shoud be accurate to within 0.125 MOA So you can know whether to round up or down to the next click.

From the need to be accurate to with 0.125 MOA one can back into the accuracy of the measuring unit. It is not the distance that is important it is the drop that is important

If you wish to look up some arcane and really boring mathematical theory google up "significant digits". If your scope is only accurate to two digits then you should proceed accordingly. While that sounds simple there are very long and tediuos books written on this subject and two or three times in my life as an engineer it has actually been important.

There are thoughts in my mind about how to solve your problem and I am sure Catshooter or Gustavo can also answer your question just as easily as me. I am not an expert on the subject but I can help you with it if you wish. My email is in my profile

For my own personal use, I only believe accuracy is needed to the one or two degree level because my shooting skills are not much better than that. /ubbthreads/images/graemlins/confused.gif I use an inclinometer from a compass and carry a cosine card for conversions and do math in my head. And then I add or subtract clicks by "intuition". What a lousy scientist I am.

5. ### BuffalobobWriters Guild

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Well, I typed too long and talked to my wife about "America's Got Talent" meanwhile Catshooter got straight to the point.

6. ### GustavoWriters Guild

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Catshooter, Mikecr and BuffaloBob said very, very logical and rightful things.

I agree 100% with every paragraph they wrote down.

Just be aware that the "cosine rule" is "good enough" in general terms, if the range is no more than 300 yards ( give or take ) and if we are talking strictly on accurate methods and devices to aid for this "angle compensation" business.

If I were you, I'll go with an angle indicator.

regards, Gus

7. ### Jeff In TXWell-Known Member

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[ QUOTE ]

Just be aware that the "cosine rule" is "good enough" in general terms, if the range is no more than 300 yards ( give or take ) and if we are talking strictly on accurate methods and devices to aid for this "angle compensation" business.
ds

[/ QUOTE ]
1+

IMHO uing a cosine angle past 400 yards is a waste of time, effort and ammo unless you're going to use the shot as a spotter to make correctionson for the follow up shot. Your % of first round hits will be very low using a cosine angle.