Kents comparison between settlement surveys and current measurements made me think of my early surveys on a small island in Bass Strait.
The wind would roar for days straight from the Antarctic.
With little option but to survey the chain would be at full catenary except it would be up and not down.
Problem! How much sag to apply?
I'd measure and re measure, pulling 15 lbs and from an educated assumption decide the sag used or applied was same as if in no wind and the chain could hang vertically Down!
They were 100 Metre 1/16th of an inch bands, so pretty light.
I'd love to run the EDM over some of the lines, particularly the ones along the tops of the sand dunes we measured.
We reestablished miles of foreshore boundaries. Very enjoyable times apart from that constant howling wind.
Never experienced anything like that, but when we put the total station on distances we chained back in the '70's we find that 99% of the time we were achieving our goal of 1 part in 10,000.
Our equipment was a 300', 1/4 inch tape. We always corrected for temperature and slope. Tension - we just knew how much to pull.
Chaining v EDM
> ... but when we put the total station on distances we chained back in the '70's we find that 99% of the time we were achieving our goal of 1 part in 10,000.
Those were some enlightening times.
My employer back then had 1 EDM and three crews. Most of our work was chaining, but once or twice a week we could nab the EDM, set control and check what we had been doing. It made us all a little better at chaining.
I do remember a few rare occasions (on flat pavement) where we had chained 1300' or longer and nailed it. Generally we kept it over 1:7500. It was fun and informative.
When I worked for the Bureau of Reclamation in the 1960's, I did a lot of section breakdowns for Reservoir Boundaries using a Lufkin Highway 300' tape, plumbing waist high on each end and using a clino for the verticle angle and the traverse tables in the BLM Red Book for the correction to use. I had the opportunity to remeasure a couple of these lines in the 1980's using my HP 3800A distance meter when doing a survey for my daughter and son-in-law. One line was ¼ mile ± and the other was a ½ mile ±. The ¼ mile line was 0.05' difference from the chained distance and the ½ mile line was 0.4' difference from the chained distance. Seemed to be a good result on the chaining distances.
We were pleasantly surprised at just how accurate you could measure with our chains given calm weather.
We'd have them calibrated each year and always apply temperature and sag, always carry a spring balance handle for the tensioing.
Often we had a summer and a winter chain. We'd order them in standardised for 25° and12° or thereabouts.
> We were pleasantly surprised at just how accurate you could measure with our chains given calm weather.
> We'd have them calibrated each year and always apply temperature and sag, always carry a spring balance handle for the tensioing.
> Often we had a summer and a winter chain. We'd order them in standardised for 25° and12° or thereabouts.
For the type of work we were doing for section breakdowns, we never worried about sag and temperature correction or using a spring balance for tension. We would pull the chain to what we hoped was 30# of tension. Having worked for an old GLO Cadastral Surveyor and being taught how they did their chaining measurements with either a 5 or 8 chain tape when they were either retracing or executing the original surveys, that was an item not to worry about. They would only eye down from the rear chain over the mark and drop a hatchet or chaining pin at the front chain point, read the clino, look up the correction in the Red Book, move the drop point to the correct position from the drop point and go on their way on down the line.
In 2005, the BLM put on a demonstration in Phoenix which I drove up to watch. They laid out a triangle, set up a solar transit on one of the apexes, got the solar bearing on two legs of the triangle and chained all three legs using the method I mentioned above. After they made all their measurements, they then used a Monroe Handcrank Calculator and a Curta Calculator to reduce their notes and run a closure check. One of the APLS organization observers used a Trimble GPS unit and followed them around the triangle gathering data. He then processed his data to see how the two measurememt systems compared. The Guy that did the GPS traverse was amazed about how close they both agreed with each other. If I remember correctly there was only a miniscal variation or none at all in the traverse.
