Tunnel Datum is a datum based on Ordnance Datum used in designing tunnels which pass below sea level. By using a lower datum as the base point, negative numbers can be avoided in calculations, eliminating a possible source of mistakes.
- for the London Underground, a tunnel datum of ODN − 100m is used; thus a depth of -60m is 40 m ATD (above tunnel datum)
- for the Channel Tunnel, a tunnel datum of ODN − 200 m is used; thus a depth of -60 m is 140 m ATD
Read more about this topic: Ordnance Datum
Famous quotes containing the words tunnel and/or datum:
“It is the light
At the end of the tunnel as it might be seen
By him looking out somberly at the shower,
The picture of hope a dying man might turn away from,
Realizing that hope is something else, something concrete
You can’t have.”
—John Ashbery (b. 1927)
“Language fails not because thought fails, but because no verbal symbols can do justice to the fullness and richness of thought. If we are to continue talking about “data” in any other sense than as reflective distinctions, the original datum is always such a qualitative whole.”
—John Dewey (1859–1952)