Leica GRZ4 360° prism

The 3 faces with the arrows give you the true height, the other 3 faces are 5mm different.

86 mm (+/- 1 mm) from the bottom of the quick release to the tilting axis is standard for most Leica prisms, as indicated on the diagram. As stated above, the GRZ4 has two sets of vertical measurements, only one of which is at 86 mm.

Thank you Jim very much. So it seems then that my rod tip has worn down about 0.02' over these 15 years.

I will have to run out to my test course at Dad's barn lot to see if this knowledge helps my vertical back site errors I have been seeing lately. It may have a little to do with the 0.06' in roughly 150' or the 0.11' in about 550' but I doubt that it accounts for the majority of the error.

My new theory (with the help from my critical thinking 14 year old) is that for whatever reason the ATR is working just fine for "downhill" shots (even very slightly "downhill" like 0.015' in 150') but has some sort of blunder occurring for "uphill" shots (even very slightly "uphill").

This would explain the fact that the back site is not checking well every time. This is a vertical only problem. Horizontal is fine.

More testing to come...

Hi Brad
Have you run the check & adjust with the ATR box ticked?
Phil

> Hi Brad
> Have you run the check & adjust with the ATR box ticked?
> Phil

Yes sir, did so yesterday, with the following results (which were the same from the last time I ran the collimation/calibration field routine):

H 00 d 00' 16"
V 00 d 00' 20"

However, I did so yesterday in the "downhill" direction. So I plan to run it next in the "uphill" direction.

Thanks very much for your help.

I am still a rookie

Well, maybe it was simply a rod height problem after all.

Yesterday, using the wrong rod height (4.98') when I thought it was 5.00'. My "uphill" V measurement was 3.01', should have been 3.09' according to my auto level rod old school shots with my 11 year old rod man helping. But the "downhill" was more like 3.11'

So Today, once I realized that my rod is about 0.02' short, and adjusted accordingly, my "uphill" shot was 3.078' and my "downhill" shot was 3.075'.

When do I get to say I have left "ROOKIE" status?

I am still a rookie

A few years back when I ordered new rods I went with the Seco's that have the non-adjustable adapter on top that is sized to the brand of equipment that you're using. This eliminates the threaded adapter with the jamb nuts as a frequent source of rod height error.

Here's a picture.

Now if I start seeing backsight elevation issues, I know to change the rod tip, if that doesn't solve it then I know the instrument needs a slap.

Edit: Here's another picture of how the math works. There quick change rods are calibrated with the assumption that the center of the prism will be 150mm above the top of the rod. They have adapters sized for the standard offsets of Topcon, Leica, Trible, etc.

Brad,

The Check and Adjust procedure should only be done with a full sized circluar prism. It does not have to be a Leica prism. The reason is that the full sized circular gives the most return to the ATR system. Also, you should only do the procedure +/- 10° from 90° vertical angle. It is also important that you have the prism at 330 feet say +/- 10 feet.

Do not do the calibration with a 360° prism.

If you let me know what model instrument you have I can send you the excerpt from the manual for the procedure requirements.

> Brad,
>
> The Check and Adjust procedure should only be done with a full sized circluar prism. It does not have to be a Leica prism. The reason is that the full sized circular gives the most return to the ATR system. Also, you should only do the procedure +/- 10° from 90° vertical angle. It is also important that you have the prism at 330 feet say +/- 10 feet.
>
> Do not do the calibration with a 360° prism.
>
> If you let me know what model instrument you have I can send you the excerpt from the manual for the procedure requirements.

Thanks man.

TCA 1100

Ancient 1998 model. Old dark army green. Heavy.

I love her dearly. She has been very good to me all these years.

" It is also important that you have the prism at 330 feet say +/- 10 feet."

..great. What would have happened if some field crew member had interpreted the 330' as just some arbitrary distance close to 100M and decided to instead pace out an even 400' for the check and adjust routine ?

R.J.,

I would run the calibration "By The Book". There is no real magic about the 100 m distance specified except that the sight picture for both you and the instrument is set to something that is comfortable to the eyes and programmed into the application. Remember that the whole process depends on you telling the instrument where the center of the target is. The ATR system expects a certain picture of the return at this distance to adjust to the mechanical center of the instrument so that the computed horizontal and vertical offsets are correct when measuring.

1. Always use a full sized circular prism
2. Always used a distance of 100 meters
3. Always let the instrument acclimate to the surrounding temperature
4. Always have the instrument fully in the shade (target does not matter)
5. Always manual sight each repetition of the sightings - do not accept the sight picture that the instrument has if you have a motorized instrument and the instrument automatically turns to net sight
6. Always perform 3 sets of the readings

Brad,

I will dig this up and send it to you.