T2 striding level question.

[w***@nyx.net]

I'm not a surveyor, just a retired newspaperman with an interest
in measuring instruments, slide rules, etc . . .

I have a Wild T2 (oldstyle) with right angle viewfinders for
celestial observations.

Recently, I acquired a striding level for the instrument.

I am uncertain about the vial markings on the striding level.

Please see photo at: www.nyx.net/~wboas/strid4.jpg

Note the vial marks go from 10-30 with 20 being the middle.

I would have expected 0 in the middle with 10 at either end.

I have not seen a good treatise about using the striding level on
the T2. Could someone point me in the right direction? Why is the
vial marked such, what is the sensitivity per division, and how
does one figure out whether the striding level is in adjustment?

Any help appreciated.

Bill
***@nyx.net

[P***@gmail.com]

Post by w***@nyx.net
I am uncertain about the vial markings on the striding level.
Please see photo at: www.nyx.net/~wboas/strid4.jpg
Note the vial marks go from 10-30 with 20 being the middle.

First, check that description of a Wild-Heerbrugg level: "Tubular level
sensitivity. Empfindlichkeit der Röhrenlibelle : 10'' per 2 mm" at
http://www.wild-heerbrugg.com/wild_n3.htm

and

"The precision of a 1 km double levelling run is quoted as ± 2 mm. The
sensitivity of the level bubble is 30" / 2 mm and the accuracy of
levelling the line of sight is ± 0,75"."

Source:
http://www.gmat.unsw.edu.au/currentstudents/ug/projects/f_pall/html/l7.html

[P***@gmail.com]

And "level sensitivity explained":
http://www.leveldevelopments.com/sensitivity-explained.htm

[Richard]

Post by w***@nyx.net
I have not seen a good treatise about using the striding level
on the T2. Could someone point me in the right direction? Why
is the vial marked such, what is the sensitivity per division,
and how does one figure out whether the striding level is in
adjustment?

Well . . . I think there is a drawing of your level in a tree
diagram of accessories at:
<Loading Image...>
located five levels above the T2 drawing in the main theodolite
box. Note that it is located in the fifth level above the box
outline, but is actually the first drawing directly above.

Would this be your T2, the NT2 model at
<Loading Image...>?

You might try balancing the striding level at right angles to its
usual position on the horizontal axis, and have it sit along the
scope instead. Looking at the difference in V readings as you
move the SL bubble the 2mm distance from line to line should
(when averaged over about ten in a row) give you some idea of
the sensitivity. Maybe.

Good luck.

[Paul Hirose]

Post by w***@nyx.net
I am uncertain about the vial markings on the striding level.
Note the vial marks go from 10-30 with 20 being the middle.

My 1959 U.S. Coast & Geodetic Survey manual ("Geodetic Triangulation")
says the striding level bubble position must be recorded after each
pointing if the line of sight is more than 5° off horizontal. The
level must be placed so the lowest numbered graduation is closest to
the vertical circle, and both ends of the bubble must be read and
recorded. If the graduations were labeled symmetrically this process
would be more goof-prone.

Those instructions were written for the old Parkhurst theodolite. Have
you looked around the Internet for a Wild T2 manual? I got one on
eBay, though unfortunately for you it's for the new style T2. It says
the striding level accessory is no longer used due to the introduction
of the compensator.

Try this to check the level's sensitivity. Set up the theodolite so
two footscrews are at right angles to the line of sight to a suitable
target, and the remaining footscrew points away from the target.

Level the instrument in the normal manner.

Set the telescope at right angles to the target.

Put the striding level in place and record the reading at one end of
the bubble.

Sight the target in the scope and note the vertical circle reading.

Tilt the scope slightly to change the vertical circle reading by some
convenient angle, amounting to a few divisions on the striding level.
Maybe 30 seconds?

Re-center the target in the crosshairs by turning the one footscrew
that's not at right angles to the target. What you've done is alter
the instrument's leveling by a known amount.

Turn the scope at right angles to the target again and note the change
in striding level bubble position.

Divide that value into the mis-leveling that you introduced. For
example, if you put the instrument 30 seconds out of level and that
moved the bubble 3 divisions, its sensitivity is 10 seconds per
division.

[l***@thinkerf.com]

Bill,

The other posts give a few clues and I can't say I have your answer -
just some more questions.

First, I'm surprized it isn't a coincidence style level. I haven't
done the math, but I thought it should be the same accuracy as the
collimating level.

Second, I assume the purpose is to adjust/compensate for the fact that
the horizontal axis is not perfectly level even after the vertical axis
is plumbed (I use the collimating coincidence level to do this very
accurately). I have a Brunson jig transit that has an adjustment in
the standards for making the horizontal axis level, but I haven't found
such an adjustment on the T2. Even the US Army Service manual doesn't
show anything, so I assume the "feinmachinen" isn't as perfect as it
should be.

Without this compensation, my T2 does not follow a plumb string line as
the scope is moved away from level (about 30 sec error at 25 deg.
azimuth). While this error is also compensated for by averaging the
direct and reversed reading, I find it annoying for machine alignment,
which is probably why a striding level is available.

In any event, the striding level should be calibrated by reversal.
Once you've done that, you should be able to compare it's sensitivity
to the base level (20"/2mm), or use the vertical scale to move the
scope off level by a known amount as one of the other posts suggested.


As stated in the other posting, I assume the max and min readings at
the end of the bubble are recorded because the length of the bubble
will change with temperature. The final reading is probably (max +
min - 20), so you get positive and negative numbers that will indicate
the direction of the lean of the axis.

Bruce

Post by w***@nyx.net
I'm not a surveyor, just a retired newspaperman with an interest
in measuring instruments, slide rules, etc . . .
I have a Wild T2 (oldstyle) with right angle viewfinders for
celestial observations.
Recently, I acquired a striding level for the instrument.
I am uncertain about the vial markings on the striding level.
Please see photo at: www.nyx.net/~wboas/strid4.jpg
Note the vial marks go from 10-30 with 20 being the middle.
I would have expected 0 in the middle with 10 at either end.
I have not seen a good treatise about using the striding level on
the T2. Could someone point me in the right direction? Why is the
vial marked such, what is the sensitivity per division, and how
does one figure out whether the striding level is in adjustment?
Any help appreciated.
Bill

[Richard]

Post by l***@thinkerf.com
First, I'm surprized it isn't a coincidence style level. I haven't
done the math, but I thought it should be the same accuracy as the
collimating level.

After market levels, as at Warren-Knight:
<http://www.warrenind.com/WKMetrology.html#Striding Level>

Post by l***@thinkerf.com
51-9045 COINCIDENCE STRIDING LEVEL, A Striding Level that uses
a coincidence type level with magnification permitting
leveling to within 1 arc second.

An old English text (Practical Field Surveying and Computations)
mentions a sensitivity of 4 arc seconds per 2mm movement of the
bubble on a striding level. Graduations similar to those shown
by the original poster are implied, but it doesn't specifiy any
particular make or model.

Post by l***@thinkerf.com
Second, I assume the purpose is to adjust/compensate for the fact that
the horizontal axis is not perfectly level even after the vertical axis
is plumbed (I use the collimating coincidence level to do this very
accurately). I have a Brunson jig transit that has an adjustment in
the standards for making the horizontal axis level, but I haven't found
such an adjustment on the T2. Even the US Army Service manual doesn't
show anything, so I assume the "feinmachinen" isn't as perfect as it
should be.

Wish I could find the cite, but I saw a claim made that there was
no method of adjusting, because there would be no wear in the
trunnion bearings, and the Wild theodolite was so accurate there
was no need for adjustment. (Yeah, one experiment is worth a
dozen theories . . . but it might have been the T3 or T4 to
which they were referring.)

Post by l***@thinkerf.com
Without this compensation, my T2 does not follow a plumb string line as
the scope is moved away from level (about 30 sec error at 25 deg.
azimuth). While this error is also compensated for by averaging the
direct and reversed reading, I find it annoying for machine alignment,
which is probably why a striding level is available.

That is an appreciable error; 1/2 inch at 100 yards. Long plumb
line at that distance.

I thought Wild ... concealed? adjusted out? ... that error by
having the operator tilt the reticle so the "vertical" line
would follow a point as the Vertical angle was increased. The
horizontal line is supposed to stay nailed to a point as the
Azimuth is changed, too. Seems to me your T2 would do one or
the other, but not both, when the vertical axis is adjusted to
be truly vertical?

Which Wild do you have? Mine is an old T21; from about 1957.
When the weather warms up a bit and the snow melts, will have to
give it a closer check. Too much wind, usually, for a long plumb
line.

[sawdoc]

Have a look at www.wild-heerbrugg.com for more info in Wild scopes.
That's where I read about the lapping done to do the final adjustment
of the axies.

My T2 is from about 1950 based on the serial number (the above site has
a lot of this type of information). I'm just testing it out in my
garage so far, so the issue of wind affecting the plumb line doesn't
apply. I do machine alignment, so I don't do long shots, but for me
1/2 minute is 0.018" at 10 feet, which in my world, you can drive a
truck through. My Brunson jig transit follows the plumb line within
0.002", and that may only be a change in diameter of the string!

I still have to check the scope against collimators, but so far it
appears to be ok. I've adjusted the horizontal and vertical
collimation to within 2 sec. when the scope is level.

Bruce

Post by Richard

Post by l***@thinkerf.com
First, I'm surprized it isn't a coincidence style level. I haven't
done the math, but I thought it should be the same accuracy as the
collimating level.

<http://www.warrenind.com/WKMetrology.html#Striding Level>

Post by l***@thinkerf.com
51-9045 COINCIDENCE STRIDING LEVEL, A Striding Level that uses
a coincidence type level with magnification permitting
leveling to within 1 arc second.

An old English text (Practical Field Surveying and Computations)
mentions a sensitivity of 4 arc seconds per 2mm movement of the
bubble on a striding level. Graduations similar to those shown
by the original poster are implied, but it doesn't specifiy any
particular make or model.

Post by l***@thinkerf.com
Second, I assume the purpose is to adjust/compensate for the fact that
the horizontal axis is not perfectly level even after the vertical axis
is plumbed (I use the collimating coincidence level to do this very
accurately). I have a Brunson jig transit that has an adjustment in
the standards for making the horizontal axis level, but I haven't found
such an adjustment on the T2. Even the US Army Service manual doesn't
show anything, so I assume the "feinmachinen" isn't as perfect as it
should be.

Wish I could find the cite, but I saw a claim made that there was
no method of adjusting, because there would be no wear in the
trunnion bearings, and the Wild theodolite was so accurate there
was no need for adjustment. (Yeah, one experiment is worth a
dozen theories . . . but it might have been the T3 or T4 to
which they were referring.)

Post by l***@thinkerf.com
Without this compensation, my T2 does not follow a plumb string line as
the scope is moved away from level (about 30 sec error at 25 deg.
azimuth). While this error is also compensated for by averaging the
direct and reversed reading, I find it annoying for machine alignment,
which is probably why a striding level is available.

That is an appreciable error; 1/2 inch at 100 yards. Long plumb
line at that distance.
I thought Wild ... concealed? adjusted out? ... that error by
having the operator tilt the reticle so the "vertical" line
would follow a point as the Vertical angle was increased. The
horizontal line is supposed to stay nailed to a point as the
Azimuth is changed, too. Seems to me your T2 would do one or
the other, but not both, when the vertical axis is adjusted to
be truly vertical?
Which Wild do you have? Mine is an old T21; from about 1957.
When the weather warms up a bit and the snow melts, will have to
give it a closer check. Too much wind, usually, for a long plumb
line.
--
Richard, 2006-Oct-31 8:21:06 PM GMT - 6 hours for summer

[Richard]

Post by sawdoc
Have a look at www.wild-heerbrugg.com for more info in Wild
scopes. That's where I read about the lapping done to do the
final adjustment of the axies.

Thanks, I will do that tomorrow.

I just happened to download and read a (rather large) pdf from
the 1980 Hewlett Packard archives:
<http://www.hparchive.com/Journals/Low-Resolution/HPJ-1980-09-Low-Resolution.pdf>
... that gives a set of diagrams on what tolerances they had on
the bearings, the trunnion machining, the effect of the tilt
caused by unequal standard heights (expressed in arc seconds) on
the Az angles . . . and much more. This was an internal
write-up on the design and manufacture of one of the first total
stations, the HP 3820A. Also shows drawings of the
[mercury/oil/parallel-face-glass-cover] cell used for the two
axis compensation; and how the segmented arcs on the glass
plates are scanned to give a sub-second readout. They were
justly proud of their work. Kind of off topic, too new to
really hold my interest, but it might be a useful comparison to
the old Wild methods and tolerances.

Take care,

[Richard]

Post by sawdoc
I do machine alignment, so I don't do long shots, but for me
1/2 minute is 0.018" at 10 feet, which in my world, you can drive a
truck through. My Brunson jig transit follows the plumb line within
0.002", and that may only be a change in diameter of the string!

Quite a difference; again makes me think there is something wrong
with the T2, especially in light of the accuracy you have managed
in your adjustments of Hz and V collimation.

Post by sawdoc
I still have to check the scope against collimators, but so far it
appears to be ok. I've adjusted the horizontal and vertical
collimation to within 2 sec. when the scope is level.

You have good eyes and a steady hand. :-)

Do you find the reading to a point 5 or 10 feet away is different
than one done at a target 100 yards away? I have a Kern DKM-2A
which seems to be aligned properly within a couple of seconds of
the perfect 180 degrees different if I plunge and turn at 100
yards; but noticed I'm maybe 15 seconds off at about a five foot
distance. I had been using the same starting point of close to
<000 d - 00 m - 10 sec> face left in both cases to use the same
part of the horizontal circle out of habit and for easier
arithmetic. Seems to me the optical axis or crosshairs are not
quite aligned with the center of the vertical axis. I have been
hesitating about moving the reticle horizontally, because I
think that would throw off my 100 yard zero, but I've not
thought it through.

I suppose I should do more short distance tests with different Hz
starting points, and see if the effect is still there, or is due
to eccentricity of the glass disk. If the disk is off, could be
I should find and use the best spot for my adjustments in future;
although I *think* the fact that the Kern and Wild both use
diametrically opposite graduations combined for the Hz reading
should eliminate that requirement.


By the way, I have looked for about an hour on that
<www.wild-heerbrugg.com> site (which I have visited frequently,
as I realized when I opened the home page) and I couldn't find
the part about construction of the T2 until I entered
<"Wild-Heerbrugg" +lapping> in a Google search. First hit was
this, picked out of the <www.wild-heerbrugg.com> site; thought
others may like it:

==========quote from TCA2300==========

Gone are the days of the Feinmechanik lapping T2 standards to
ensure a perfect tilting axis. Until the advent of on-board
compensation for axis errors, theodolite standards were slowly
and meticulously ?lapped? (scraped and ground by hand) until the
trunnion axis was absolutely perpendicular to the standing axis.
With present day high-accuracy theodolites and total stations,
the standards are engineered to be just as stable as the T2, but
the mechanical adjustment is ?close enough.? After manufacturing,
the standards are tested to verify that they meet manufacturing
tolerances. Then an electronic adjustment is performed, saving
hours of manufacturing while producing an even more accurate
instrument. As an added advantage, the tilting axis calibration
can be checked and adjusted in the field.

I was introduced to sub-second alignment techniques at Rockwell
International by Ned Cherry, a guru in the aerospace alignment
field. Once, while working with a highly sensitive gyroscope
component, I noticed the display reading the hundredths of an
arc-second was fluctuating as we walked around, despite the fact
that we were working on a 3-foot-thick concrete slab that
measured 20 x 25 feet. Ned remarked, ?Below 0.1 arc second
everything turns to Jello.? To this end, the TCA2003 has been
constructed using proprietary materials and engineered using the
latest finite element analysis techniques. Every Leica instrument
is tested and calibrated for -4?F to + 122?F to ensure that
accuracy specifications are met.

===========end quote=========

Google is (sometimes) good. Thanks again.