Patent ID: 7789171

Claim:
A system for measuring a property of a downhole apparatus over a longitudinal extent of the downhole apparatus, the system comprising: a first sensor coupled to the downhole apparatus at a first location, the first sensor providing an output which is a measure of an orientation of the downhole apparatus at the first location; a second sensor coupled to the downhole apparatus at a second location, the second sensor providing an output which is a measure of an orientation of the downhole apparatus at the second location; a device for: accepting A=the output of the first sensor representing the orientation of the downhole apparatus at the first location at a first time and B=the output of the first sensor representing the orientation of the downhole apparatus at the first location at a second time, the second time being later than the first time; accepting C=the output of the second sensor representing the orientation of the downhole apparatus at the second location at the first time and D=the output of the second sensor representing the orientation of the downhole apparatus at the second location at the second time; determining an angle φ b between A and C; determining an angle φ r between B and D; and computing the property of the downhole apparatus using φ b and φ r .