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GPS is NOT accurate enough for surveying purposes, any surveyor will tell you this, a good surveyor will be spot on, GPS is only accuarate for within around one foot for military GPS and within a yard or so for civilian GPS. I used to know the tolerances, But the marks as other posters stated, survey bench marks.

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We had them all over underground, but they were sprayed on the roof with paint, with a circle around the survey pin.

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  • 4 weeks later...

Scribbled on a piece of paper found in my anorak pocket; Benchmarks, in feet. Toll Bridge far side 78.9 Trent Bridge first bay 95 South corner Cattle Market Rd 89.5 Smithy Row North 122 The Talbot 130 Brewhouse Yard gate 87.6 Weekday Cross 130 St Mary's steps 149 Theatre Royal 164 St Andrews Mans Rd 258 at the Castle Gate 136 upper College St/Derby Rd 213 Gen Hosp gate (near wall postbox) 197 top of Park Steps 206 pumphouse 5 Ropewalk 262 Canning Circ police stn 256 Bluebell Hill 227 lost gatepost opp Castle Grove (probably equal to bottom of Park Steps) 140

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  • 2 months later...

You could draw a reasonably accurate contour map with that little lot!

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