The tangential method is the simplest calculation among other directional survey calculations.
The tangential method formulas are listed below;
Tangential Method Calculation formula
Where;
MD = Measured Depth between surveys in ft
I1 = Inclination (angle) of upper survey in degrees
I2 = Inclination (angle) of lower in degrees
Az1= Azimuth direction of upper survey
Az2 = Azimuth direction of lower survey
The following example is the Tangential Method Calculation.
Survey 1
Depth = 3500 ft
Inclination = 15 degree (I1)
Azimuth = 20 degree (Az1)
Survey 2
Depth = 3600 ft
Inclination = 25 degree (I2)
Azimuth = 45 degree (Az2)
Solution:
MD = 3600 – 3500 = 100 ft
As per the formulas above, you will get answers as listed below;
North = 29.88 ft
East = 29.88 ft
TVD = 90.63 ft
Please find the Excel sheet used for The 
Tangential Method Calculation
Reference books: Directional Drilling Books
Formulas and Calculations for Drilling, Production and Workover, Second Edition
i acknowlegde this site for their work well done.
There are several methods that can be used to calculate the survey data, of these some are accurate while are other may produce some error for a given situation.
Some of the most common methods used for survey calculation in the industry are:
Tangential method (Least Accurate)
Balanced Tangential method
Average Angle method
Radius of Curvature method (Most Accurate)
Minimum Curvature method (Most Accurate)
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xls file is password protected. plz give me that password
Which sheet do you need to be unprotected? I can do it for you but I cannot give you the password.