Fix incorrenct indexing

src/display/core/predictive.h

@@ -22,7 +22,7 @@ class VolumetricRateCalculator {
 
         size_t i = measurementTimes.size();
         double cutoff = time - windowDuration;
-        while (measurementTimes[i - 1] > cutoff) { // check from the most recent time
+        while (i > 0 && measurementTimes[i - 1] > cutoff) { // check from the most recent time
             i--;
         }
         // i is the index of the first entry after the cutoff
@@ -42,9 +42,15 @@ class VolumetricRateCalculator {
         double tdev2 = 0.0;
         double tdev_vdev = 0.0;
         for (size_t j = i; j < measurements.size(); j++) {
-            tdev_vdev += (measurementTimes[i] - t_mean) * (measurements[i] - v_mean);
-            tdev2 += pow(measurementTimes[i] - t_mean, 2.0);
+            tdev_vdev += (measurementTimes[j] - t_mean) * (measurements[j] - v_mean);
+            tdev2 += pow(measurementTimes[j] - t_mean, 2.0);
         }
+
+        // Prevent division by zero
+        if (tdev2 < 1e-10) {
+            return 0.0;
+        }
+
         double volumePerMilliSecond = tdev_vdev / tdev2;              // the slope (volume per millisecond) of the linear best fit
         return volumePerMilliSecond > 0 ? volumePerMilliSecond : 0.0; // return 0 if it is not positive, convert to seconds
     }
@@ -53,7 +59,14 @@ class VolumetricRateCalculator {
         if (measurementTimes.size() < 2)
             return 0.0;
         double overshoot = actualVolume - expectedVolume;
-        return overshoot / getRate(measurementTimes.back());
+        double rate = getRate(measurementTimes.back());
+
+        // Prevent division by zero
+        if (rate < 1e-10) {
+            return 0.0;
+        }
+
+        return overshoot / rate;
     }
 
   private: