**Dave,**

I assume your problem is a result of using a GPS that gives you a flat land, or a "base" distance only unlike a rangefinder does.

If I understand you correctly, you are atempting to find the moa setting for a zero at 200yds "line of sight" (LOS) at a 45° angle.
This is exactly correct.

**Basing this on the "base" 141yd distance or the LOS 200yd distance would give an incorrect moa setting.**
Again, this is correct.

**The 141yd setting (only the GPS gives) would, yes cause a below LOS impact. **

The 200yd setting (the laser RF gives) would, cause a classic above LOS impact.
Correct again.

**What you want to do is convert the base distance to actual (laser) distance so you can then correct for the 45° angle, which the later part the Oehler Ballistic Explorer program does, true?**
I'm a little fuzzy here. I don't have the Oehler Ballistics Explorer software so I'm unfamiliar with it's functioning.

By using the 141 yard "base" distance in conjunction with my elevation readings from the GPS I KNOW the "slope" or distance that a LASER RF would indicate. It's the Pythagorean theorem (A squared + B squared = C squared) thing.

Remember that I have both the target's GPS fix and the shooter's GPS fix, these fixes also give me elevation. I get the height of the triangle leg by the difference in the two elevations and the length of the base from the difference in flat land distance.

**And you want to do this using known data from a GPS and something that measures the angle for you, without having to ever know the actual LOS distance, correct?**
The computer computes the angle from the two sets of data, 2 postions and 2 geographic elevations. I have the height and base lengths. The height and base angle is always 90 degrees because the center of the earth is directly below us.

**But, I'm probably wrong because you used a 200yd range in your last post so should I assume you're using a rangefinder now also?**
I'm sure you've got it figured out now but I state it anyway. No I still haven't used a LASER RF.

**I admit, I am a little confused about why you were trying to incorperate the "base" distance into this, then abandoned it in the end? Were you simply trying to figure the 45° angle into the "come ups"?**
The "base" distance is the DISTANCE gravity will act on the bullet.

**I also came up with 10.6" total drop and 1.81 MOA correction at 200yds on both programs I have using your specs at standard pressure. Also the BC "Load From A Disk" gives is .496 for that speed. **

BTW, what do you use for measuring the angle and where do you buy one?
With two GPS fixes and the elevation at those fixed points you can calculate the angle with a pocket calculator.

** Also how do you figure the "cosine" for the angle as you did here (.707)? I looked up cosine in the dictionary an it said I had to know trigonometry to figure it, which is obvious now that I don't. Feel like giving a lesson? If so go SLOW.**
I'm pretty good at going slow, I spend so much time tripping over the obvious that I barely make any headway ever. [img]images/icons/grin.gif[/img]

Here's a cosine table and a link (the link is a PDF).

angle cosine

10 .9848

15 .9659

20 .9397

25 .9063

30 .8660

35 .8192

40 .7660

45 .7071

50 .6429

55 .5736

60 .5

65 .4226

70 .3420

75 .2588

80 .1736

85 .0872

http://api.ctcd.cc.tx.us/consume/a104gm8.PDF
**Dave, what does the astrisk signify (*) in the "=10.1 * .707" you wrote? is this another sign for multiplication? I assume it is as the "7.14 inches" answer you gave is arived at by this.**
Yes, it the sign for multiplication.

**Sorry, I hope I haven't confused anyone. I only intended to clarify a few points as this is something I have been wondering about this last week but have not brought up yet, but Dave opened the door now.**

You are the one who often mentions the slope angle or cosine in posts and has recently been nagging at me because I don't understand enough about how to calculate it's effect without the computer program or how to measure it while in the field. We will be hunting below some steep mountain sides this fall so it maybe necessary to figure in.
I'm always trying to understand how to better my chances at making a first round hit from calculated data.

You can make a little angle indicator for field use by using a plastic protractor, a piece of string and a weight. The MilDot Master has a provision for doing this too.