The everyday name for the round metal disk, usually brass or bronze, that forms the top of most survey and tidal bench marks. Each cap is stamped with an identifier and often a warning against disturbing it. Field crews talk about finding, shooting and closing on brass caps, and a cap that has been bent, reset or paved over is worthless until it is re-levelled.
Found the brass cap under the dock ramp, stamping matches the datum sheet, set the rod on it.
Also heard as
- disk
- survey disk
- monument
Related terms
Bench mark
A permanent, stable mark of known height near a tide station that preserves the station's datums.
Recovery
Finding an existing bench mark in the field, checking its condition and reporting it as found, damaged or lost.
Leveling
Precise measurement of height differences between bench marks and the gauge or staff using a level and rods.
Closing the loop
Finishing a level run back on the starting bench mark to measure how much error crept in.