# What is the method of calculation reduced level

Upendra Kumar

There are two methods available at a reduced level.

1. The collimation system or height of the instrument system
2. The rise and fall system.

In this method find the elevation of the
height of instrument for every set up of the instrument and then obtain the reduced levels of points
with reference to the respective height of the instrument.

The height of the instrument or line of collimation is determined by adding the back sight staff reading to
the benchmark and the reduced level of intermediate and change point is found by subtracting the
respective staff reading from the height of the instrument.

 POINT B.S I.S F.S H.I R.L REMARK B.M 1.255 101.255 100.000 A 1.750 99.505 B 2.150 2.750 100.655 98.505 C 1.950 98.750 D 1.550 99.105

In the above figure and table
In the first setting.
Reduced level of H.I at B.M=100.000+1.255=101.255
Reduced level of point A =101.255-1.755=    99.505
Reduced level of point B =101.255-2.750=    98.505
In the second set.
Reduced level of H.I at point B=98.505+2.150=100.655
Reduced level of point C =100.655-1.950=98.750
Reduced level of point D =100.655-1.550=99.105

Arithmetical check:- Sum of B.S-Sum of F.S=Last RL-First RL
=3.405-4.300=99.105-100.000
=-0.895 =-0.895

In this method the difference of level between two points are
determined by consecutive points by comparing each point after the first with that immediately
preceding it.

If the staff reading of the forward point is smaller than the immediately preceding staff reading then
the difference is added from the preceding point RL.

If the staff reading of forward point is greater than the immediately preceding staff reading then the
the difference is subtracted from the preceding point RL.

 POINT B.S I.S F.S RISE FALL R.L REMARK B.M 0.75 100.00 A 1.25 0.50 99.500 B 2.75 1.50 98.000 C 1.50 1.25 99.250 D 1.75 0.25 99.000

The difference of point A with respect B.M= 0.75-1.25=-0.50   (FALL)
Difference of point B with respect A =1.25-2.75 =- 1.50     (FALL)
Difference of point C with respect B =2.75-1.50 =1.25       (RISE)
Difference of point D with respect C=1.50-1.75 =- 0.25     (FALL)

Then the reduced level of A = 100-0.5=99.500
Then the reduced level of B = 99.500-1.50=98.000
Then the reduced level of C = 98.000+1.25=99.250
Then the reduced level of D = 99.25-0.25=99.000

Arithmetical check:- Sum of B.S-Sum of F.S=  Sum of rise-Sum of fall=Last RL-First RL
0.75- 1.75= 1.25-2.25=99.000-100.00
= -1.00 =-1.00= -1.000