diff --git a/src/specificClass.js b/src/specificClass.js
index 636f678..d34e6cc 100644
--- a/src/specificClass.js
+++ b/src/specificClass.js
@@ -323,7 +323,7 @@ class Reactor_PFR extends Reactor {
   _updateMeasurement(measurementType, value, position, context) {
     switch(measurementType) {
       case "quantity (oxygen)":
-        grid_pos = Math.round(position / this.config.length * this.n_x);
+        let grid_pos = Math.round(position / this.config.length * this.n_x);
         this.state[grid_pos][S_O_INDEX] = value; // naive approach for reconciling measurements and simulation
         break;
       default: