diff --git a/src/yyy_data/core.clj b/src/yyy_data/core.clj
index c7e53c9..3ca6219 100644
--- a/src/yyy_data/core.clj
+++ b/src/yyy_data/core.clj
@@ -404,21 +404,22 @@
       n²    (expt n 2)
       n³    (expt n 3)
       [M φ] (loop  [φ φ0 M 0]
+              ;; the error is in this loop somewhere..
               (let
                 ;; φ = (N-N0-M)/(a*F0) + φ;
                 [φ₁ (+' φ (/ (-' N N0 M) (*' a F0)))
                  ;; (φ-φ0)
-                 Δφ (-' φ φ0)
+                 Δφ (-' φ₁ φ0)
                  ;; var Ma = (1 + n + (5/4)*n2 + (5/4)*n3) * (φ-φ0);
                  Ma (*' (+' 1 n (*' 5/4 n²) (*' 5/4 n³)) Δφ)
                  ;; var Mb = (3*n + 3*n*n + (21/8)*n3) * Math.sin(φ-φ0) * Math.cos(φ+φ0);
-                 Mb (*' (+' (*' n 3) (*' n² 3) (*' 21/8 n³)) (sin Δφ) (cos (+' φ φ0)))
+                 Mb (*' (+' (*' n 3) (*' n² 3) (*' 21/8 n³)) (sin Δφ) (cos (+' φ₁ φ0)))
                  ;; var Mc = ((15/8)*n2 + (15/8)*n3) * Math.sin(2*(φ-φ0)) * Math.cos(2*(φ+φ0));
-                 Mc (*' (+' (*' n² 15/8) (*' n³ 15/8)) (sin (*' 2 Δφ)) (cos (*' 2 (+' φ φ0))))
+                 Mc (*' (+' (*' n² 15/8) (*' n³ 15/8)) (sin (*' 2 Δφ)) (cos (*' 2 (+' φ₁ φ0))))
                  ;; var Md = (35/24)*n3 * Math.sin(3*(φ-φ0)) * Math.cos(3*(φ+φ0));
-                 Md (*' 35/24 n³ (sin (*' 3 Δφ)) (cos (*' 3 (+' φ φ0))))
-                 M₁ (*' b F0 (+' (-' 0 Ma) Mb Mc (-' 0 Md)))]
-                (println (str "loop: φ: " φ "; M: " M "; termination: " (-' N N0 M₁)))
+                 Md (*' 35/24 n³ (sin (*' 3 Δφ)) (cos (*' 3 (+' φ₁ φ0))))
+                 ;; M = b * F0 * (Ma - Mb + Mc - Md);
+                 M₁ (*' b F0 (+' (-' Ma Mb) (-' Mc Md)))]
                 (if
                   (>= (-' N N0 M₁) 0.00001)
                   (recur φ₁ M₁)