Tmoa, smoa?

adamsgt

adamsgt

Jerry Adams
Trying to figure out how to use the "Output Units" block on the Applied Ballistics Profile Loader. It handles Mil, TMOA, SMOA, and Clicks. Did a Google search for TMOA and came up with The Monastery of Ages, Trademark Owners Association, Telangana Meeseva Operators Association, The Muslims Of America and The Movies On-Air. Finally found that TMOA stands for True Minute Of Arc and SMOA stands for Shooters Minute of Arc. Not sure what SMOA really means.

Anyway, my Nightforce scope manual says that the clicks are .125 true MOA so that means that 8 clicks equals 1.047 inches at 100 yards. Did I get that part right?
 
And SMOA has become accepted as 1.000 inch at 100 yards. So in today's world of playing long range and people are checking scopes for tracking based on design parameters, a 30 minutes "come up" of adjustment for a true MOA scope is 31.41 inches vs a SMOA scope which would be only 30 inches. We have advanced in technology today to such a level of precision that it can make a difference. Is not shooting fun?
 
adamsgt said:
Trying to figure out how to use the "Output Units" block on the Applied Ballistics Profile Loader. It handles Mil, TMOA, SMOA, and Clicks. Did a Google search for TMOA and came up with The Monastery of Ages, Trademark Owners Association, Telangana Meeseva Operators Association, The Muslims Of America and The Movies On-Air. Finally found that TMOA stands for True Minute Of Arc and SMOA stands for Shooters Minute of Arc. Not sure what SMOA really means.

Anyway, my Nightforce scope manual says that the clicks are .125 true MOA so that means that 8 clicks equals 1.047 inches at 100 yards. Did I get that part right?
Click to expand...

The math behind MOA is taught in basic surveying which is applying what was learned in trig. You convert 1 minute of angle to decimal degrees by dividing one by 60 = .016666667 as far as you want to carry the 6's. Sin = the length of the leg of the triangle opposite the angle over the adjacent length of the triangle. The sin of 0.01666666666666666666666666666667punched into a calculator =0.00029088820456342459637429741574. Take the sin number (0.00029088820456342459637429741574)* 3600 inches in 100 yards = 1.047197536428328546947470696664. Which is your 1.047" at 100 yards. We did a lot of that kind of thing when we were running transits in college in surveying. At the time, you either had to look up the sin of an angle in a table in a book or if you happened to have a caculcator that would convert degrees, minutes, seconds to decimal degrees and then do trig functions, that made it a lot easier. Calculators were in their infancy when I was in college and I had a TI SR-51 that was one of the first scientific calculators. Think it was about $80. It made surveying class easy.
 
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Mike Bryant said:
The math behind MOA is taught in basic surveying which is applying what was learned in trig. You convert 1 minute of angle to decimal degrees by dividing one by 60 = .016666667 as far as you want to carry the 6's. Sin = the length of the leg of the triangle opposite the angle over the adjacent length of the triangle. The sin of 0.01666666666666666666666666666667punched into a calculator =0.00029088820456342459637429741574. Take the sin number (0.00029088820456342459637429741574)* 3600 inches in 100 yards = 1.047197536428328546947470696664. Which is your 1.047" at 100 yards. We did a lot of that kind of thing when we were running transits in college in surveying. At the time, you either had to look up the sin of an angle in a table in a book or if you happened to have a caculcator that would convert degrees, minutes, seconds to decimal degrees and then do trig functions, that made it a lot easier. Calculators were in their infancy when I was in college and I had a TI SR-51 that was one of the first scientific calculators. Think it was about $80. It made surveying class easy.
Click to expand...
I had a HP 21 that featured RPN (reverse Polish notation...no equal sign) It cost $125, for a basic scientific calculator. Back in the day, I managed to end up in an advanced math class class in the 7th grade. Our teacher had an engineering background. We learned trig, which in 1961 required the use of printed tables. We also learned about logarithms and the basics of using a slide rule. How's that for old? Because of those experiences I had a real appreciation for the advantages of my old HP.
 
Boyd,

I hate to admit it but got my engineering degree using a slide rule. But I was not a Luddite, a couple of years later when HP came out with the first "scientific calculator" the HP35 I managed to buy serial number 13.
 
Fred Bohl said:
Boyd,

I hate to admit it but got my engineering degree using a slide rule. But I was not a Luddite, a couple of years later when HP came out with the first "scientific calculator" the HP35 I managed to buy serial number 13.
Click to expand...
I've still got three slide rules sitting in a box in my workshop. One of the best features of a slide rule is that it taught you to know where to put the decimal place when you got your answer.
 
Back to the original question. TMOA apparently stands for true minute of angle (1.047"@ 100 yd.). SMOA would then be shooting minute of angle (1" @ 100 yd) TMOA is 4.7% larger than SMOA, but we can be equally accurate working with either unit, if we know which was used to take our measurements, and we understand the value of each.
On the calculation of MOA at 100 yards, only the definition of pi is required, and its value to however many places you require. For those that may have forgotten, pi is the ratio of the circumference of a circle to its diameter. If we convert 100 yards to inches (since that is the unit that we want for our answer) it is 3,600 inches...times two gives the diameter of a circle of 100 yard radius. That diameter times pi, gives the circumference of that circle, dividing that circumference by 360 gives the length along the arc of one degree, and dividing that by 60 the length along the arc of one MOA. For practical purposes the difference between the straight line between the two points on an arc that define one MOA and the distance following the curve of the arc can be ignored. Thanks to pocket calculators all of this is much quicker to do than write.
 
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adamsgt said:
I've still got three slide rules sitting in a box in my workshop. One of the best features of a slide rule is that it taught you to know where to put the decimal place when you got your answer.
Click to expand...

I have a really nice Post bamboo slide rule in my shop desk. It's mainly there because I don't know where else to put it and don't want to throw it away. Definitely antique or close to it depending upon how old something has to be to be classified as antique. Obsolete for sure. Not being able to replace the battery pack in the TI calculator took care of it.
 
Slide rules and calculators

Mike Bryant said:
I have a really nice Post bamboo slide rule in my shop desk. It's mainly there because I don't know where else to put it and don't want to throw it away. Definitely antique or close to it depending upon how old something has to be to be classified as antique. Obsolete for sure. Not being able to replace the battery pack in the TI calculator took care of it.
Click to expand...

Still have a scientific TI but my first field calculator was a Curtis. Great for trig functions and logarithms but for me too easy to make mistakes on.

If you liked mechanical things it definitely had a cool factor. It was sometimes referred too as the Coffee Grinder.

Mort
 
Mike Bryant said:
The math behind MOA is taught in basic surveying which is applying what was learned in trig. You convert 1 minute of angle to decimal degrees by dividing one by 60 = .016666667 as far as you want to carry the 6's. Sin = the length of the leg of the triangle opposite the angle over the adjacent length of the triangle. The sin of 0.01666666666666666666666666666667punched into a calculator =0.00029088820456342459637429741574. Take the sin number (0.00029088820456342459637429741574)* 3600 inches in 100 yards = 1.047197536428328546947470696664. Which is your 1.047" at 100 yards. We did a lot of that kind of thing when we were running transits in college in surveying. At the time, you either had to look up the sin of an angle in a table in a book or if you happened to have a caculcator that would convert degrees, minutes, seconds to decimal degrees and then do trig functions, that made it a lot easier. Calculators were in their infancy when I was in college and I had a TI SR-51 that was one of the first scientific calculators. Think it was about $80. It made surveying class easy.
Click to expand...
Mike, by adjacent length, don't you mean the hypotenuse of the triangle? I realize when talking about 1 MOA, one is looking at a very "skinny" triangle, with the right angle at 100 yards. Old Chief "SOH CAH TOA" got me through Trig back in the old days, and yes I had a K&E bamboo slide rule....which I hated. Good shooting....James
 
Soh cah toa

JDMock said:
Mike, by adjacent length, don't you mean the hypotenuse of the triangle? I realize when talking about 1 MOA, one is looking at a very "skinny" triangle, with the right angle at 100 yards. Old Chief "SOH CAH TOA" got me through Trig back in the old days, and yes I had a K&E bamboo slide rule....which I hated. Good shooting....James
Click to expand...

I struggled with Algebra and Geometry but Trig made sense....I could visualize it and "SOH CAH TOA " made problem solving much easier.

I went on line and looked up the Curtis calculator. It was invented by someone in a German P.O.W. camp.

I didn't own the Curtis I used. They were very expensive.
 
Transit and Tape

Mike Bryant said:
The math behind MOA is taught in basic surveying which is applying what was learned in trig. You convert 1 minute of angle to decimal degrees by dividing one by 60 = .016666667 as far as you want to carry the 6's. Sin = the length of the leg of the triangle opposite the angle over the adjacent length of the triangle. The sin of 0.01666666666666666666666666666667punched into a calculator =0.00029088820456342459637429741574. Take the sin number (0.00029088820456342459637429741574)* 3600 inches in 100 yards = 1.047197536428328546947470696664. Which is your 1.047" at 100 yards. We did a lot of that kind of thing when we were running transits in college in surveying. At the time, you either had to look up the sin of an angle in a table in a book or if you happened to have a caculcator that would convert degrees, minutes, seconds to decimal degrees and then do trig functions, that made it a lot easier. Calculators were in their infancy when I was in college and I had a TI SR-51 that was one of the first scientific calculators. Think it was about $80. It made surveying class easy.
Click to expand...

What kind of transit did you use in school? A T16 maybe?
A steel tape and tension gauge for distance ?....just curious.
 
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