A buddy of mine(about 80 years old or so), borrows another's buddy's LOCUS units from time to time to do simple GPS. He won't borrow my PM2's, cause they're too complicated . . . comparatively.

I think he likes the LOCUS because it's all together in a simple package(he likes simple) . . . he doesn't like the "complicated" IR download though.

ANYWAY, he did some GPS work for a flood cert, using a local BenchMark . . . which was placed in the past few years, on a bridge which was removed & replaced(losing the old RM disk(NGVD29)).

NOW . . . he needed to find out what datum the new disk is on, since it was set by a private contractor and no indication of the datum is on the drawings.(we were thinking they might've offset the old disk and then brough the same datum-based elevation back in).

ANYWAY . . . I helped him by showing him how to use CORS data(18 miles distance) to do a check, thinking a couple of tenths might give him an indication of which datum was actually used.

The elevation agreed within 0.03 feet.

NOW, for the good part.

He only used one tripod(near the house), and on the benchmark, he physically placed the LOCUS unit . . . he had a vertical height of 0.64 feet, on the wingwall of a bridge, on a busy state route, with trees in the area.

The next point(a spot check which he missed by 0.30 feet(I think the road's been repaved since 1999, the date of the spot elevation) . . . the LOCUST reported high, which would make sense.

ANYWAY . . . I sorta chuckled, cause during this, what should've been a fiasco session, he got a call from ODOT(Ohio), informing him that the BM was NAVD88.

The session on the tripod was for 45 minutes, the session on the BM was about 35 minutes and the session on the spot was 20 minutes . . . oh yeh, the all red-vectored from the CORS at 18+ miles.

SOMETIMES, this stuff still amazes me.

BTW, I told him to get longer sessions, get the units up into the air a little more and that I still found it hard to accept that kind of . . . accuracy(?) on a 35 minute session at 18 miles.

Just though someone would like to know . . .