Find square-root using Newton method in Scheme

newton_sqrt.scm

(define (average x y)
  (* (+ x y) 0.5))

(define (good_enough? guess x)
  (< (abs (- x (* guess guess))) 0.001))

(define (improve guess x)
  (average guess (/ x guess)))

(define (sqrt_itr guess x)
  (if (good_enough? guess x)
      guess
      (sqrt_itr (improve guess x) x)))

(define (newton_sqrt x)
  (sqrt_itr 1.0 x))

; use MIT-Scheme to test codes above
; $ scheme
; > (cf "newton_sqrt")
; > (load "newton_sqrt.scm")
; > (newton_sqrt 4.0)
; ;Value: 2.0000000929222947
; > (newton_sqrt 1000.0)
; ;Value: 31.622782450701045