diff --git a/index.js b/index.js
index dded213..54bc8de 100644
--- a/index.js
+++ b/index.js
@@ -12,6 +12,7 @@ const outputUtils = require('./src/helper/outputUtils.js');
 const logger = require('./src/helper/logger.js');
 const validation = require('./src/helper/validationUtils.js');
 const configUtils = require('./src/helper/configUtils.js');
+const assertions = require('./src/helper/assertionUtils.js')
 
 // Domain-specific modules
 const { MeasurementContainer } = require('./src/measurements/index.js');
@@ -34,6 +35,7 @@ module.exports = {
     configUtils,
     logger,
     validation,
+    assertions,
     MeasurementContainer,
     nrmse,
     state,
diff --git a/src/measurements/MeasurementContainer.js b/src/measurements/MeasurementContainer.js
index 20099f8..516e182 100644
--- a/src/measurements/MeasurementContainer.js
+++ b/src/measurements/MeasurementContainer.js
@@ -88,11 +88,18 @@ class MeasurementContainer {
     return this;
   }
 
-  position(positionName) {
+  position(positionValue) {
     if (!this._currentVariant) {
       throw new Error('Variant must be specified before position');
     }
-    this._currentPosition = positionName;
+
+    // Turn string positions into numeric values
+    if (typeof positionValue == "string") {
+      positionValue = this._convertPositionStr2Num(positionValue);
+    }
+
+    this._currentPosition = positionValue;
+    
     return this;
   }
 
@@ -243,10 +250,12 @@ class MeasurementContainer {
     const savedPosition = this._currentPosition;
     
     // Get upstream and downstream measurements
-    this._currentPosition = 'upstream';
+    const positions = this.getPositions();
+
+    this._currentPosition = Math.min(...positions);
     const upstream = this.get();
     
-    this._currentPosition = 'downstream';
+    this._currentPosition = Math.max(...positions);
     const downstream = this.get();
     
     this._currentPosition = savedPosition;
@@ -319,7 +328,7 @@ class MeasurementContainer {
       Object.keys(this.measurements[this._currentType]) : [];
   }
 
-  getPositions() {
+  getPositions(asNumber = false) {
     if (!this._currentType || !this._currentVariant) {
       throw new Error('Type and variant must be specified before listing positions');
     }
@@ -328,8 +337,12 @@ class MeasurementContainer {
         !this.measurements[this._currentType][this._currentVariant]) {
       return [];
     }
-    
-    return Object.keys(this.measurements[this._currentType][this._currentVariant]);
+
+    if (asNumber) {
+      return Object.keys(this.measurements[this._currentType][this._currentVariant]);
+    }
+
+    return Object.keys(this.measurements[this._currentType][this._currentVariant]).map(this._convertPositionNum2Str);
   }
 
   clear() {
@@ -404,6 +417,34 @@ class MeasurementContainer {
     }
   }
 
+  _convertPositionStr2Num(positionString) {
+    switch(positionString) {
+      case "atEquipment":
+        return 0;
+      case "upstream":
+        return Number.POSITIVE_INFINITY;
+      case "downstream":
+        return Number.NEGATIVE_INFINITY;
+      
+      default:
+        this.logger.error(`Invalid positionVsParent provided: ${positionString}`);
+        return;
+    }
+  }
+
+  _convertPositionNum2Str(positionValue) {
+    if (positionValue === 0) {
+      return "atEquipment";
+    }
+    if (positionValue < 0) {
+      return "upstream";
+    }
+    if (positionValue > 0) {
+      return "downstream";
+    }
+    this.logger.error(`Invalid position provided: ${positionValue}`);
+  }
+
 }
 
 module.exports = MeasurementContainer;