tenthjester65 asked me to explain it but not sure I can adequately but will try.
In my case it was an easy way to keep track of the backsight with a 2-man crew that had to double our angles saving someone from having to go back to the backsight for a shot all the time. You still need to get the initial shot for distance and angle of course. Once that was done my bud would stick a nail in a tree nearby (close on line of possible) so I could sight it for a angle check.
The order of how you are taking your shots and flopping the scope would depend as well. In our case we were doing BS, FS, flop, BS and FS. Someone has to do a lot of walking. If you were doing a BS, flop, BS then FS flop and FS you wouldn't need so much walking or the deadman.
Hey all you other fellers out there, was that about right?
Please chime in and correct me or add to that.
(I could have shown how we did that lots quicker than it took me to write all that.)
E
We called it stacking a lath. Took a back site and zero on the point (use tripod, plum bob or prism pole) then guided the rodman to set a lath behind and right edge on line. Check line to the point before rodman left to insure instrument was stable.
Dallas I still do this only we set an 8d nail in the top of the stake online and wrap it with flagging.
Aloha, Dallas and SCCC:
Could you I accomplish the same with fixed backsight prism? Just wondering if this is just different way to accomplishing the same goal? Thank you.
> Could you I accomplish the same with fixed backsight prism?
Certainly. Using a lath or nail or some other expendable device for a backsight is simply a means to reduce the amount of equipment that one has to haul around. In steep or brushy country this can save a lot of time and manpower.
> > Could you I accomplish the same with fixed backsight prism?
>
> Certainly. Using a lath or nail or some other expendable device for a backsight is simply a means to reduce the amount of equipment that one has to haul around. In steep or brushy country this can save a lot of time and manpower.
Aloha, Jim:
That makes a lot of sense. Thank you!
Using a lath backsight is common practice around here, especially with a 2 man crew.
When working in the woods, you wouldn't get very much done in a day if you had to pack around 3 sets of legs or walk to the backsight every time.
The instrument man will set his own lath backsight before he moves ahead (using the optical plummet. Some prefer to make a vertical line with a sharpy, while other sight a specific edge of the lath (left or right side). If for some reason the view to the lath is obstructed (common), after moving ahead - Inst. is zero'd on a plumb bob string and a lath is set further behind the mark. If your lucky enough, there may be a log or tree limb that you can set a nail in.
I have never heard it called any special name, just a backsight.
>sight a specific edge of the lath (left or right side)
For precise work, it is always advisable to have a symmetrical target and not an edge. The eye doesn't do as well in finding an edge as it does a center, under a lot of lighting conditions.
> Using a lath backsight is common practice around here, especially with a 2 man crew.
>
> When working in the woods, you wouldn't get very much done in a day if you had to pack around 3 sets of legs or walk to the backsight every time.
>
> The instrument man will set his own lath backsight before he moves ahead (using the optical plummet. Some prefer to make a vertical line with a sharpy, while other sight a specific edge of the lath (left or right side). If for some reason the view to the lath is obstructed (common), after moving ahead - Inst. is zero'd on a plumb bob string and a lath is set further behind the mark. If your lucky enough, there may be a log or tree limb that you can set a nail in.
>
> I have never heard it called any special name, just a backsight.
Aloha, Imaudigger:
Thanks for the additional input.
I guess if one is carrying elevation for a particular survey, then this method cannot be used right? Rod person got to go the spot.
>
> I guess if one is carrying elevation for a particular survey, then this method cannot be used right? Rod person got to go the spot.
Simply use a folding rule to measure a height from the surface point and mark a horizontal line on the lath. Record the backsite vertical/zenith angle to the line. When data is being reduced the surface point elevation is computed, height of mark is added. The slight horizontal offset should not drastically alter the accuracy of the trig levels.
> >sight a specific edge of the lath (left or right side)
>
> For precise work, it is always advisable to have a symmetrical target and not an edge. The eye doesn't do as well in finding an edge as it does a center, under a lot of lighting conditions.
I agree and always use a vertical line in the center of the lath. That way, on the longer length backsights, you can center on the lath.
I do know several people that always use the edge. Never understood why, seems like your adding room for a blunder if someone else sets the backsight.
We always used to refer to it as setting a picket. Find a nice straight stick (usually from the brush pile as you cut line), sharpen both ends, and drive it in after taking your backsight with the rod and prism.
Saved a lot of time and walking when cutting line.
