I believe that is the same as the MECHANICS RULE, a method of approx. The square Root. To find the Square Root, an estimate is made first and used as the divisor, the approx. Square Root is the average of the quotient (your answer by division), and the original estimate.
Ex: Find the Sq.Rt of 180.(follow along by doing the division on paper) Estimate 13, since 12 x 12 = 144, and 14 x 14 = 196. So, 180 Divided by 13 = 1 first, subtract 12 from 18 and get 5, bring down the 0 to get 50. Next answer is a 3 as 3 x 13 is 39. Subtract that from 50 to get 11. Bring down another zero to get 110. Try 8. 8 x 13 = 104, subtract that from 111 to get 7 bring down another zero to make 70...try 5, 5 x 13 = 65. Subtract from 70 to get 5. Stop there. Your estimated answer is 13.85. Average 13 and 13.85 and you get 13. 425 a very good approximation to the square root of 180.
To Review: You guessed the square root of 180 to be about 13. You did the division by 13 and got 13.85. You averaged 13.85 and 13 (add them and divide by 2) and you got 13.425, the square root of 180.
Ex: Find the Sq.Rt of 180.(follow along by doing the division on paper) Estimate 13, since 12 x 12 = 144, and 14 x 14 = 196. So, 180 Divided by 13 = 1 first, subtract 12 from 18 and get 5, bring down the 0 to get 50. Next answer is a 3 as 3 x 13 is 39. Subtract that from 50 to get 11. Bring down another zero to get 110. Try 8. 8 x 13 = 104, subtract that from 111 to get 7 bring down another zero to make 70...try 5, 5 x 13 = 65. Subtract from 70 to get 5. Stop there. Your estimated answer is 13.85. Average 13 and 13.85 and you get 13. 425 a very good approximation to the square root of 180.
To Review: You guessed the square root of 180 to be about 13. You did the division by 13 and got 13.85. You averaged 13.85 and 13 (add them and divide by 2) and you got 13.425, the square root of 180.