:good: 😀
My first reaction is that they had a chain that was poorly repaired (like a link replaced); or a chain that was built with slightly different-sized links; or maybe one of the crew members held his end of the chain consistently on the wrong spot. I have a couple of old chains and I am not sure exactly where I would hold the plumb bob, or drop my chaining pin from.
> Perhaps he is referring to Nate's comment in this [msg=91575]old thread[/msg]?
>
> I took that comment to have picked an arbitrary number different from 1320, and not to say that there were a lot with that particular non-ideal value.
That would be the very one!
Unlike you, though I thought: "Hmmm. There's a lesson in there! What is the significance of precisely that number? It's got to be some multiple of a Chain, a rod a link; maybe some Vara transformation"
Silly me. I never suspected Nate just made up a number! I do tend to over think things a lot. I'm fascinated by all the replies though. Those "instructions to Surveyors" or whatever they're called are very very interesting.
> I am not sure exactly where I would hold the plumb bob, or drop my chaining pin from
Well, get them out and measure them against your best modern method. Gotta keep your equipment in calibration. 😛
The ones I've seen used, which isn't many, were intended to measure from extreme end of handle to end of handle.
Wear was a significant issue for a working chain, as well as stretching if it snagged while being carried. With almost 600 wearing surfaces in a typical 4-pole chain a couple thousandths of an inch per surface becomes 0.1 ft per chain, or 1:660, almost the whole error budget for the mid-1800's. That's why the instructions came to require the deputy to have two chains, and compare the working one against his standard chain that was not otherwise used.
After thinking about this overnite...perhaps the equipment wasn't as much to blame as the "random and true" method of surveying. They ran a random line between two monuments and then corrected their lines based on their mis-tie. Unlike modern surveys, they didn't leave accurate traverse points behind to correct from; just a temporary post at the half-way point. This point was then corrected for both line and distance.
I've seen mis-ties along section boundaries recorded from 20-150 links (13.2'-99').
What do you guys think?
:good:
Good post. I think I'll pull out the chain and measure the last link distance. IT should be easy to see where on the handle they intended to take the measurement from. I just hadn't thought about it much until this thread.
