Who knows why people do the things they do. Maybe someone checked into the mon's with their survey equip. and decided to mark the caps where their stakeout location indicated. Or maybe someone thought they were set up over the center during an occupation and then discovered after the session that they weren't centered over the cap. So they marked the location on the cap for future reference in case they needed it. Possibly done by a "somewhat inexperienced" Caltrans crew. (just kidding Rob!)
Of course, as you can see, placing unauthorized marks on NGS caps causes confusion and is not recommended.
Ambiguous U.S.C. & G.S. monuments
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Jim Frame
- Posts: 1599
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Are you sure the "extra" mark was a punch and not an air release hole? At one time the practice at NGS (or maybe it was still USC&GS) was to drill a small off-center hole in the disk to allow air to escape as the disk was seated in the grout. The theory was that this would ensure a complete seal between the grout and the underside of the disk. The practice was subsequently abandoned, but there are a lot of disks out there with air release holes in addition to the centered measurement point.
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