diff --git a/.github/workflows/test.yaml b/.github/workflows/test.yaml
index a8aa140..599cf76 100644
--- a/.github/workflows/test.yaml
+++ b/.github/workflows/test.yaml
@@ -26,6 +26,55 @@ jobs:
                     run  --rm  --user root 
                     zorm-test-github-actions
 
+    vallum:
+        runs-on: ubuntu-latest
+        services:
+            postgres:
+                image: postgres
+                ports:
+                    - 5432:5432
+                env:
+                    POSTGRES_PASSWORD: postgres
+                options: >-
+                    --health-cmd pg_isready
+                    --health-interval 10s
+                    --health-timeout 5s
+                    --health-retries 5
+
+        steps:
+            -   uses: actions/checkout@v4
+                with:
+                    fetch-depth: 0
+            -   name: Setup Gradle
+                uses: gradle/actions/setup-gradle@v3
+            -   name: backward-compatibility-test
+                run: ./vallum/backward-compatibility-test.sh
+                env:
+                    POSTGRES_URL: jdbc:postgresql://localhost:5432/postgres
+                    POSTGRES_USER: postgres
+                    POSTGRES_PASSWORD: postgres
+                    BASE_URL: http://localhost:8082
+                    CORS_ALLOW_ORIGIN_PATTERN: 'http://localhost:\d{2,5}'
+                    # Keycloak test realm JWK
+                    ACCESS_TOKEN_JWK: |
+                        {
+                            "kid": "n-X5BeXFe6pIXhDBsDu2mQ2VYc23RSZCFRU5Y6IuzC8",
+                            "kty": "OKP",
+                            "alg": "EdDSA",
+                            "use": "sig",
+                            "crv": "Ed25519",
+                            "x": "ILokSbk8EKH-Q1aWo_TguuDRccoSVfEbmGSbm5gcn5I"
+                        }
+                    USER_ID: f9eee559-7bd8-4a53-99cf-aaef36dad8a1
+                    CLIENT_ID: test-client-ztor-api
+                    CLIENT_SECRET: ${{ secrets.KEYCLOAK_TEST_CLIENT_SECRET }}
+            -   name: upload-test-results
+                if: always()
+                uses: actions/upload-artifact@v4
+                with:
+                    name: test-results
+                    path: ./vallum/build/reports/tests/test/
+
     # Tests without a database
     gradle:
         runs-on: ubuntu-latest
diff --git a/compose.yaml b/compose.yaml
index 80db9aa..5c561e6 100644
--- a/compose.yaml
+++ b/compose.yaml
@@ -181,7 +181,7 @@ services:
     vallum-test:
         extends:
             service: gradle-base
-        command: vallum:test
+        entrypoint: ./vallum/backward-compatibility-test.sh
         volumes:
             - gradle-vallum-test-cache:/home/gradle/.gradle
         depends_on:
diff --git a/frontend/src/components/company-survey-v2/time-series/interval-dropdown.tsx b/frontend/src/components/company-survey-v2/time-series/interval-dropdown.tsx
deleted file mode 100644
index e15fa8b..0000000
--- a/frontend/src/components/company-survey-v2/time-series/interval-dropdown.tsx
+++ /dev/null
@@ -1,29 +0,0 @@
-import {FunctionComponent} from "react"
-import {Dropdown} from "primereact/dropdown"
-import {isoStringToDateTimeUnit, dateTimeUnitToIsoString} from "zero-zummon"
-import {SelectItem, SelectItemOptionsType} from "primereact/selectitem"
-
-const options: SelectItemOptionsType = [
-    {
-        value: "PT15M",
-        label: "Kwartier",
-    },
-    {
-        value: "P1D",
-        label: "Dag",
-    },
-    {
-        value: "P1M",
-        label: "Maand",
-    },
-]
-
-export const IntervalDropdown: FunctionComponent<{
-    timeStep: any,
-    setTimeStep: (timeStep: any) => void
-}> = ({timeStep, setTimeStep}) => {
-
-    return (
-        <Dropdown options={options} value={dateTimeUnitToIsoString(timeStep)} onChange={event => setTimeStep(isoStringToDateTimeUnit(event.value))}/>
-    )
-}
diff --git a/frontend/src/components/company-survey-v2/time-series/time-series-textarea.tsx b/frontend/src/components/company-survey-v2/time-series/time-series-textarea.tsx
index 2c8e923..cd50c3d 100644
--- a/frontend/src/components/company-survey-v2/time-series/time-series-textarea.tsx
+++ b/frontend/src/components/company-survey-v2/time-series/time-series-textarea.tsx
@@ -7,7 +7,6 @@ import {LabelRow} from "../generic/label-row"
 import {displayTimeZone, kotlinInstantToJsJodaInstant, prettyPrint} from "./time-series-util"
 import {Dropdown} from "primereact/dropdown"
 import {InputText} from "primereact/inputtext"
-import {IntervalDropdown} from "./interval-dropdown"
 
 const placeholder = `
 bijvoorbeeld:
@@ -51,9 +50,6 @@ export const TimeSeriesTextarea: FunctionComponent<{timeSeries: TimeSeries, setT
             <LabelRow label="Tijdzone">
                 <Dropdown options={[{ label: 'Nederlandse tijd', value: displayTimeZone }]} value={displayTimeZone}/>
             </LabelRow>
-            <LabelRow label="Meetinterval">
-                <IntervalDropdown timeStep={internalTimeSeries.timeStep} setTimeStep={timeStep => setTimeSeriesImpl(internalTimeSeries.withTimeStep(timeStep))} />
-            </LabelRow>
             <LabelRow label="Plak hier de waarden in kWh">
                 <InputTextarea
                     id="values"
diff --git a/vallum/backward-compatibility-test.sh b/vallum/backward-compatibility-test.sh
new file mode 100755
index 0000000..d988c5f
--- /dev/null
+++ b/vallum/backward-compatibility-test.sh
@@ -0,0 +1,26 @@
+#!/bin/bash
+set -ex
+
+# This verifies that the latest version of Ztor works with older versions of Vallum.
+# Probably there is a more flexible way of testing this using different ClassLoaders instead of
+
+CURRENT=$(git branch --show-current)
+
+if [[ -z $CURRENT ]]; then
+    CURRENT=$(git rev-parse HEAD)
+fi
+
+mkdir -p shadowJar
+gradle vallum:shadowJar
+mv vallum/build/libs/vallum-dev-all.jar shadowJar/vallum-current-all.jar
+
+git switch --detach 14c1cb1
+gradle vallum:shadowJar
+mv vallum/build/libs/vallum-dev-all.jar shadowJar/vallum-14c1cb1-all.jar
+
+git switch production
+gradle vallum:shadowJar
+mv vallum/build/libs/vallum-dev-all.jar shadowJar/vallum-production-all.jar
+
+git switch --detach $CURRENT
+gradle vallum:test
diff --git a/vallum/src/test/java/com/zenmo/vallum/BackwardCompatibilityTest.java b/vallum/src/test/java/com/zenmo/vallum/BackwardCompatibilityTest.java
new file mode 100644
index 0000000..e7587e6
--- /dev/null
+++ b/vallum/src/test/java/com/zenmo/vallum/BackwardCompatibilityTest.java
@@ -0,0 +1,54 @@
+package com.zenmo.vallum;
+
+import java.io.File;
+import java.io.IOException;
+import java.lang.reflect.InvocationTargetException;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class BackwardCompatibilityTest {
+    @Test
+    public void test() throws IOException, ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {
+        String[] shadowJarPaths = {
+                "../shadowJar/vallum-14c1cb1-all.jar",
+                "../shadowJar/vallum-production-all.jar",
+                "../shadowJar/vallum-current-all.jar",
+        };
+
+        var stopZtor = InitKt.initZtor(8082);
+
+        for (var shadowJarPath: shadowJarPaths) {
+            testVallumVersion(shadowJarPath);
+        }
+
+        stopZtor.stop();
+    }
+
+    public void testVallumVersion(String shadowJarPath) throws IOException, ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {
+        File jarFile = new File(shadowJarPath).getCanonicalFile();
+        System.out.println(jarFile.getPath());
+        if (!jarFile.exists()) {
+            throw new RuntimeException("Jarfile doesnt exist");
+        }
+        URL jarUrl = jarFile.toURI().toURL();
+        URL[] urls = {jarUrl};
+        var loader = new URLClassLoader(urls, null);
+
+        var vallumClass = loader.loadClass("com.zenmo.vallum.Vallum");
+        var constructor = vallumClass.getDeclaredConstructor(String.class, String.class, String.class, String.class);
+        var oldVallum = constructor.newInstance(System.getenv("CLIENT_ID"), System.getenv("CLIENT_SECRET"), "http://localhost:8082", "https://keycloak.zenmo.com/realms/testrealm/protocol/openid-connect/token");
+
+        /*
+         * TODO: write the code like normal java rather then reflection.
+         * I don't know how to do this with this class loader stuff
+         */
+        var getSurveysByProject = vallumClass.getMethod("getSurveysByProject", String.class);
+        var surveys = (List) getSurveysByProject.invoke(oldVallum, "Waardkwartier");
+        assertEquals(1, surveys.size());
+    }
+}
diff --git a/vallum/src/test/java/VallumTest.java b/vallum/src/test/java/com/zenmo/vallum/VallumTest.java
similarity index 94%
rename from vallum/src/test/java/VallumTest.java
rename to vallum/src/test/java/com/zenmo/vallum/VallumTest.java
index dcfe084..4208429 100644
--- a/vallum/src/test/java/VallumTest.java
+++ b/vallum/src/test/java/com/zenmo/vallum/VallumTest.java
@@ -1,3 +1,5 @@
+package com.zenmo.vallum;
+
 import com.zenmo.vallum.Vallum;
 import com.zenmo.zummon.companysurvey.Address;
 import com.zenmo.zummon.companysurvey.GridConnection;
@@ -14,12 +16,13 @@
 public class VallumTest {
     @Test
     public void test() {
-        var stopZtor = InitKt.initZtor();
+        var port = 8083;
+        var stopZtor = InitKt.initZtor(port);
 
         Vallum vallum = new Vallum(
                 System.getenv("CLIENT_ID"),
                 System.getenv("CLIENT_SECRET"),
-                "http://localhost:8082",
+                "http://localhost:" + port,
                 "https://keycloak.zenmo.com/realms/testrealm/protocol/openid-connect/token"
         );
 
@@ -61,4 +64,5 @@ public void test() {
 
         stopZtor.stop();
     }
+
 }
diff --git a/vallum/src/test/kotlin/Init.kt b/vallum/src/test/kotlin/Init.kt
index 78ffc8d..a0d009b 100644
--- a/vallum/src/test/kotlin/Init.kt
+++ b/vallum/src/test/kotlin/Init.kt
@@ -1,3 +1,5 @@
+package com.zenmo.vallum
+
 import com.zenmo.orm.companysurvey.ProjectRepository
 import com.zenmo.orm.companysurvey.SurveyRepository
 import com.zenmo.orm.companysurvey.createMockSurvey
@@ -12,7 +14,8 @@ import org.jetbrains.exposed.sql.SchemaUtils
 import org.jetbrains.exposed.sql.transactions.transaction
 import java.util.*
 
-fun initZtor(): StopZtor {
+@JvmOverloads
+fun initZtor(port: Int = 8082): StopZtor {
     val db = connectToPostgres()
     val schema = Schema(db.connector().schema)
     transaction(db) {
@@ -36,5 +39,7 @@ fun initZtor(): StopZtor {
     surveyRepository.save(createMockSurvey(projectName1))
     surveyRepository.save(createMockSurvey(projectName2))
 
-    return startTestServer()
+    return startTestServer(port)
 }
+
+
diff --git a/ztor/src/main/kotlin/com/zenmo/ztor/Application.kt b/ztor/src/main/kotlin/com/zenmo/ztor/Application.kt
index e76ef5c..fcfa931 100644
--- a/ztor/src/main/kotlin/com/zenmo/ztor/Application.kt
+++ b/ztor/src/main/kotlin/com/zenmo/ztor/Application.kt
@@ -50,27 +50,6 @@ fun main(args: Array<String>) {
             .start(wait = true)
 }
 
-fun interface StopZtor {
-    fun stop(): Unit
-}
-
-fun startTestServer(): StopZtor {
-    val server = embeddedServer(Netty, port = 8082, host = "0.0.0.0", module = Application::vallumMinimal)
-        .start(wait = false)
-
-    return StopZtor { server.stop(1000, 1000) }
-}
-
-fun Application.vallumMinimal() {
-    configureHTTP()
-    configureMonitoring()
-    configureSerialization()
-    configureAuthentication()
-    val db = configureDatabases()
-    configureRouting()
-    configureStatusPages()
-}
-
 fun Application.module() {
     configureHTTP()
     configureMonitoring()
diff --git a/ztor/src/main/kotlin/com/zenmo/ztor/TestServer.kt b/ztor/src/main/kotlin/com/zenmo/ztor/TestServer.kt
new file mode 100644
index 0000000..f7963d7
--- /dev/null
+++ b/ztor/src/main/kotlin/com/zenmo/ztor/TestServer.kt
@@ -0,0 +1,28 @@
+package com.zenmo.ztor
+
+import com.zenmo.ztor.plugins.*
+import io.ktor.server.application.*
+import io.ktor.server.engine.*
+import io.ktor.server.netty.*
+
+fun interface StopZtor {
+    fun stop(): Unit
+}
+
+@JvmOverloads
+fun startTestServer(port: Int = 8082): StopZtor {
+    val server = embeddedServer(Netty, port = port, host = "0.0.0.0", module = Application::vallumMinimal)
+        .start(wait = false)
+
+    return StopZtor { server.stop(1000, 1000) }
+}
+
+fun Application.vallumMinimal() {
+    configureHTTP()
+    configureMonitoring()
+    configureSerialization()
+    configureAuthentication()
+    val db = configureDatabases()
+    configureRouting()
+    configureStatusPages()
+}