Method of determining tacheometric constants in the field1) A fairly level ground is selected. The tacheometer is set up at O. Vertical angle is kept zero and pegs are fixed at A, B & C, known distances apart. 2) The staff intercepts (stadia hair readings) are noted at each of the pegs. Let these intercepts be S1, S2 & S3. 3) The horizontal distances of the pegs from O are actually measured. Let these distances be D1, D2 & D3. 4) By substituting the values of D1, D2, D3 and S1, S2, S3 in general equation D = (f/i) S + (f+d) We get a number of equations, as follows D1 = (f/i) S1 + (f+d) D2 = (f/i) S2 + (f+d) and so on. 5) By solving the equations in pairs, we get number of values tacheometric constants (f/i) and (f+d) 6) Average of (f/i) and of (f+d) as obtained above, gives values of constants.