Work on #108

src/pab/pab.ts

 import { CalculatorType } from "../compute-node";
+import { ParamValueMode } from "../index";
 import { Nub } from "../nub";
 import { ParamCalculability, ParamDefinition } from "../param/param-definition";
 import { IParamDefinitionIterator, ParamsEquation, ParamsEquationArrayIterator } from "../param/params-equation";
@@ -253,6 +254,20 @@ export class Pab extends Nub {
         this.downWall.reinitResult();
     }
 
+    /**
+     * Only Q and Z1 are calculable (see #108)
+     */
+    public findFirstCalculableParameter(otherThan?: ParamDefinition) {
+        for (const p of [ this.prms.Q, this.prms.Z1 ]) {
+            if (p !== otherThan
+                && p.valueMode !== ParamValueMode.CALCUL // event LINK might be reset here
+            ) {
+                return p;
+            }
+        }
+        throw new Error(`PAB : no calculable parameter found other than ${otherThan ? otherThan.symbol : "undefined"}`);
+    }
+
     /**
      * paramétrage de la calculabilité des paramètres
      */