Larry Scott, post: 442435, member: 8766 wrote: "Turning angles by turning the fine motion always CW."
I have never found any justification in that practice. If I need back off a micro radian, I back off a micro radian. T1/T2/T3/T16, glass plate, micrometer or not. When averaging sets just beware of an outlier.
Kent McMillan, post: 442440, member: 3 wrote: I think that it originated in a much earlier generation of theodolites that were prone to "jump" as the tangent screw was loosened, hence moving the tangent motion in the direction that compressed the spring was considered best practice. Wasn't this in Bomford? I could cheat and look, but that's my vague recollection.
speaking of more modern instruments, i tried this method in my total station angular testing and did not detect any effect. what did make a good deal of difference, however, was always moving the scope upwards or downwards as the last vertical movement. The telescope on several newer and older leica total stations had about 2" of slop side to side. always moving the scope upwards or downwards as the final movement was one of the key parts of getting to consistent, sub-second precision. eg. move roughly to target, move scope upwards, then position horizontally.
Larry Scott, post: 442441, member: 8766 wrote:
I just think only CW isn't as objective,
i would agree with this statement. if your best bisection of the target lands on ACW movement then go with it. I think your sets would be better off for being able to choose from the group of best possible pointings, not just the group of best CW pointings. Providing, of course, your instrument doesn't have some kind of funky eccentric movement caused by tangent screws and locks.
Sergeant Schultz, post: 442359, member: 315 wrote: ?????
Sarge,
That was our way of communicating with the guy on the other end of the chain. There always has to be tension on a chrome-clad steel tape, chain to me. Each guy is responsible for applying the appropriate tension to make that 100 footer a hundred feet long, right? Often times, if you are trying to maintain a level chain, a guy isn't always to able to brace himself without doing a little grunting or holding of the breath.
In my case, it was mandatory for the rear chairman to notify the head chairman, as precisely as possible, when he was "GOOD". What I am saying is when I am holding mid-chest, at 25 pounds of pull, to set a point, I was incapable of communicating to the other guy the instant that my peach billy (former trainee's words) was exactly over my point without letting a squirt of air past my lips in the form a loud word or noise, thereby causing me to move from the point. Happened every time for me. Braced against the knee at 45 feet doesn't bother me.
I was taught to place the finger nail of my index finger, which was right there to hold the peach billy string anyway, and sort of pluck the chain. Similar to how a Flamenco Guitarist does. A properly tensioned and supported chain makes a sweet "ping" sound that travels at the speed of OMG to the other end where that guy understands it to mean "GOOD".
I would like to hear from others if they did (do) this.
I was pretty good throwing the peach billy, too. Punched many a poor slob's tool. Amazing how far a point can go into a peach billy when you hit 'em dead on.
JA, PLS SoCal
Kent McMillan, post: 442440, member: 3 wrote: I think that it originated in a much earlier generation of theodolites that were prone to "jump" as the tangent screw was loosened, hence moving the tangent motion in the direction that compressed the spring was considered best practice. Wasn't this in Bomford? I could cheat and look, but that's my vague recollection.
Along with tangent screw etiquette...
Older, micrometer guns. Do you determine the micrometer scale error as part of every set? And prorate the micrometer measurement in angle reduction?
Larry Scott, post: 442454, member: 8766 wrote: Along with tangent screw etiquette...
Older, micrometer guns. Do you determine the micrometer scale error as part of every set? And prorate the micrometer measurement in angle reduction?
I never did, but the run error in a Zeiss Th2 never seemed to be significant.
Kent McMillan, post: 442455, member: 3 wrote: I never did, but the run error in a Zeiss Th2 never seemed to be significant.
I had a network and Starnet wanted to assign a lot negative residuals, independent of distance to target (T2). After days of pondering, I found the residual followed the minutes of angle. In any one set, the increasing micrometer sweeps and the decreasing sweeps added up to 9:55", not 10:00". My T3 adds up to a reliable 120.5".
So I've heard "always sweep the micrometer the same direction". Which induces systematic error.
I always turn and even number of sets with the micrometer swept increasing and decreasing. Prorating the micrometer as much as 5" to as little as several 1/10s"
The residuals to angles went to 0-1" much of the time.
Just curious if that's something you'd encountered.
Larry Scott, post: 442459, member: 8766 wrote: The residuals to angles went to 0-1" much of the time.
Just curious if that's something you'd encountered.
I had read about micrometer run error and checked the Th2s I've owned expecting to find it. But I never did.
I was taught to only turn the tangent screw to the right and stop when on target.
It was because we were using mechanical instruments that only needed an electric current to light the night sky to read the vernier and the less slop in the turn the better the results.
This was done to eliminate as much instrument error possible and pass on to operator error if not correctly on target.
Without covers, today's electronic marvels hardly resemble their predecessors, except for perhaps the focal length of the lenses involved.
I believe the adjustment knobs are simply kept the same principal so everyone can maintain their past skills.
My recommendation is to use what has worked best for everyone.
For those that have never found the magic connection with your instrument, keep practicing.
Jerry Attrick, post: 442452, member: 1585 wrote: I was pretty good throwing the peach billy, too. Punched many a poor slob's tool. Amazing how far a point can go into a peach billy when you hit 'em dead on.
Peach billy ?????