Column layout is a layout mechanism that spans across container boundaries, arranging content on a common grid consisting of a fixed number of columns and a variable number of rows.
We use a total station for laying out. It is an electronic and optical instrument that accurately lays out buildings using discrete points.
A total station can measure angles and distances electronically and process trigonometrically to give us the minimum position coordinates in space.
Tolerance of total station: a typical total station can measure distance upto 1500 meters (4900ft) with an accuracy of about 1.5mm.
Cross Hair: This is done by placing very fine points within the telescope and these fine points is a obtained by the intersection of two very fine lines placed in the common focus of the object glass in front of the eyepieces. These lines are called crosshairs.
The cross hairs are best made of platinum wires.