Error Ratio
"Error Ratio" also known as "Separation Factor" is used for assessing the collision risk of two wellbores. It is calculated as a ratio of center-to-center distance and the sum of semi-major axis of error ellipse of the two wellbores. An error Ratio of 1 indicates that the error ellipses of the two well bores touch each other. Error Ratio of less than 1 means that error ellipses overlap and Error Ratio of more than 1 means that the ellipses don't overlap.