Fix nnls logic.

If no latest target exists, the deficit is zero (no target, no
problem).

1 files changed, 3 insertions, 4 deletions

diff --git a/services/nnls.rkt b/services/nnls.rkt
index 52afbad..649d416 100644
--- a/services/nnls.rkt
+++ b/services/nnls.rkt
@@ -26,17 +26,16 @@
        (define latest-target (get-latest-nutrient-target-value n))
        (define deficit
          (cond
+           [(false? latest-target)
+            0]
            [(or (false? latest-measurement)
                 (zero? latest-measurement))
             latest-target]
-           [(false? latest-target)
-            0]
            [(and (number? latest-measurement)
                  (number? latest-target))
             (* 100
                (/ (- latest-target latest-measurement)
-                  latest-measurement))]
-           [else (error "either the target or measurement are not numbers")]))
+                  latest-measurement))]))
        deficit)))
   (define error-threshold 10e-4)
   (lawson-hanson-1974 fertilizer-product-matrix deficits error-threshold))