src/measurements/Measurement.js

@@ -67,6 +67,23 @@ class Measurement {
     if (this.values.length === 0) return null;
     return this.values[this.values.length - 1];
   }
+
+  getLaggedValue(lag){
+    if(this.values.length <= lag) return null;
+    return this.values[this.values.length - lag];
+  }
+
+  getLaggedSample(lag){
+    if (lag < 0) throw new Error('lag must be >= 0');
+      const index = this.values.length - 1 - lag;
+    if (index < 0) return null;
+
+    return {
+      value: this.values[index],
+      timestamp: this.timestamps[index],
+      unit: this.unit,
+    };
+  }
   
   getAverage() {
     if (this.values.length === 0) return null;

src/measurements/MeasurementContainer.js

@@ -94,7 +94,8 @@ class MeasurementContainer {
       throw new Error('Variant must be specified before position');
     }
 
-    this._currentPosition = positionValue;
+    
+    this._currentPosition = positionValue.toString().toLowerCase();;
     
     return this;
   }
@@ -247,9 +248,31 @@ class MeasurementContainer {
     return measurement ? measurement.getAllValues() : null;
   }
 
+  getLaggedValue(lag = 1,requestedUnit = null ){
+    const measurement = this.get();
+    if (!measurement) return null;
+    
+    const value = measurement.getLaggedSample(lag);
+    if (value === null) return null;
 
-  differenceUpDown(){
+    // Return as-is if no unit conversion requested
+    if (!requestedUnit) {
+      return value;
+    }
 
+    // Convert if needed
+    if (measurement.unit && requestedUnit !== measurement.unit) {
+      try {
+        return convertModule(value).from(measurement.unit).to(requestedUnit);
+      } catch (error) {
+        if (this.logger) {
+          this.logger.error(`Unit conversion failed: ${error.message}`);
+        }
+        return value; // Return original value if conversion fails
+      }
+    }
+
+    return value;
   }
 
 

src/measurements/examples.js

@@ -214,8 +214,8 @@ const pressureDiff = basicContainer
 console.log(`Pressure difference: ${pressureDiff.value} ${pressureDiff.unit}\n`);
 
 //reversable difference
-const deltaP = measurements.type("pressure").variant("measured").difference(); // defaults to downstream - upstream
+const deltaP = basicContainer.type("pressure").variant("measured").difference(); // defaults to downstream - upstream
-const netFlow = measurements.type("flow").variant("measured").difference({ from: "upstream", to: "downstream" });
+const netFlow = basicContainer.type("flow").variant("measured").difference({ from: "upstream", to: "downstream" });
 
 // ====================================
 // ADVANCED STATISTICS & HISTORY
@@ -252,6 +252,28 @@ const allValues = stats.getAllValues();
 console.log(`  Samples: ${allValues.values.length}`);
 console.log(`  History: [${allValues.values.join(', ')}]\n`);
 
+console.log('--- Lagged sample comparison ---');
+
+const latest = stats.getCurrentValue();               // existing helper
+const prevSample = stats.getLaggedValue(1);           // new helper
+const prevPrevSample = stats.getLaggedValue(2);       // optional
+
+if (prevSample) {
+  const delta = latest - prevSample.value;
+  console.log(
+    `Current vs previous: ${latest} ${statsData.unit} (t=${stats.get().getLatestTimestamp()}) vs ` +
+    `${prevSample.value} ${prevSample.unit} (t=${prevSample.timestamp})`
+  );
+  console.log(`Δ = ${delta.toFixed(2)} ${statsData.unit}`);
+}
+
+if (prevPrevSample) {
+  console.log(
+    `Previous vs 2-steps-back timestamps: ${new Date(prevSample.timestamp).toISOString()} vs ` +
+    `${new Date(prevPrevSample.timestamp).toISOString()}`
+  );
+}
+
 // ====================================
 // DYNAMIC UNIT MANAGEMENT
 // ====================================
@@ -303,8 +325,11 @@ basicContainer.getTypes().forEach(type => {
   }
 });
 
+
+
 console.log('\n✅ All examples complete!\n');
 
+
 // ====================================
 // BEST PRACTICES
 // ====================================