diff --git a/controllers/modbus.controller.js b/controllers/modbus.controller.js
index 2596b94..712741b 100644
--- a/controllers/modbus.controller.js
+++ b/controllers/modbus.controller.js
@@ -1,6 +1,7 @@
 import db from "#root/config/database.config.js";
 import modbusClient from "#root/config/modbus-client.config.js";
 import * as utils from '#root/utils/index.js'
+import { RowNotFoundError } from '#root/errors/index.js'
 import { appService, modbusService } from "#root/services/index.js";
 
 export const modbusController = {
@@ -136,7 +137,7 @@ export const modbusController = {
   async removeDevice(req, res, next) {
     try {
       const device = await db.get(`SELECT id FROM "modbus_slaves" WHERE id = ?`, [req.body.id]);
-      if (!device) return res.status(404).json({ message: "Device not found." });
+      if (!device) throw new RowNotFoundError();
       await db.run(`DELETE FROM "modbus_slaves" WHERE id = ?`, [req.body.id]);
       return res.status(200).json({ message: "Device removed." });
     } catch (error) {
@@ -158,7 +159,12 @@ export const modbusController = {
                     VALUES (?, ?, ?, ?, ?)
                   `, [name, slave_id, reg_addr, reg_format, reg_type]
                   );
-      return res.status(200).json({ message: 'Created.' });
+      const createdDisplayValue = await db.get(`SELECT * FROM "display_values" WHERE id = last_insert_rowid()`);
+      
+      return res.status(200).json({ 
+        message: 'Created.',
+        data: createdDisplayValue,
+      });
     } catch (error) {
       next(error);
     }
@@ -179,6 +185,30 @@ export const modbusController = {
     }
   },
 
+  /**
+   * Update display value
+   * @param {import('express').Request} req
+   * @param {import('express').Response} res
+   * @param {import('express').NextFunction} next
+   */
+  async updateDisplayValue(req, res, next) {
+    try {
+      const { id, name, slave_id, reg_addr, reg_type, reg_format } = req.body;
+      const row = await db.get(`SELECT id from "display_values" WHERE id = ?`, [id]);
+      if (!row) throw new RowNotFoundError();
+      await db.run(`UPDATE "display_values" SET
+                    name = ?,
+                    slave_id = ?,
+                    reg_addr = ?,
+                    reg_type = ?,
+                    reg_format = ? 
+                    WHERE id = ?`, [name, slave_id, reg_addr, reg_type, reg_format, id]);
+      return res.status(200).json({ message: 'Updated.' });
+    } catch (error) {
+      next(error);
+    }
+  },
+
   /**
    * Creates event stream aboud modbus connection status
    * @param {import('express').Request} req
@@ -209,7 +239,7 @@ export const modbusController = {
       if (!slave_id) return res.status(400).json({ error: { message: "'slave_id' parameter is required." } });
 
       const device = await db.get(`SELECT * FROM "modbus_slaves" WHERE id = ?`, [slave_id]);
-      if (!device) return res.status(404).json({ error: { message: "Device not found." } });
+      if (!device) throw new RowNotFoundError();
 
       utils.setSSEHeaders(res);
 
diff --git a/data.db b/data.db
index 3986657..c0f7498 100644
Binary files a/data.db and b/data.db differ
diff --git a/errors/index.js b/errors/index.js
new file mode 100644
index 0000000..c4796ed
--- /dev/null
+++ b/errors/index.js
@@ -0,0 +1,14 @@
+export class DomainError extends Error {
+  constructor(message) {
+    super(message);
+    this.name = this.constructor.name;
+    Error.captureStackTrace(this, this.constructor);
+  }
+}
+
+export class RowNotFoundError extends DomainError {
+  constructor() {
+    super('Row not found.');
+    this.statusCode = 404;
+  }
+}
\ No newline at end of file
diff --git a/middlewares/error-handler.middleware.js b/middlewares/error-handler.middleware.js
index 1a0e293..8d95ee7 100644
--- a/middlewares/error-handler.middleware.js
+++ b/middlewares/error-handler.middleware.js
@@ -9,7 +9,7 @@ export function errorHandlerMiddleware() {
     req.log.error(error, "Something went wrong");
     const status = error.statusCode || 500;
     const message = error.message || "Internal Server Error";
-    res.status(500).json({
+    res.status(status).json({
       error: {
         status,
         message,
diff --git a/public/css/dist.css b/public/css/dist.css
index 62fb05d..7f16fe2 100644
--- a/public/css/dist.css
+++ b/public/css/dist.css
@@ -928,6 +928,11 @@ video {
   background-color: rgb(239 68 68 / var(--tw-bg-opacity));
 }
 
+.bg-white {
+  --tw-bg-opacity: 1;
+  background-color: rgb(255 255 255 / var(--tw-bg-opacity));
+}
+
 .fill-blue-600 {
   fill: #2563eb;
 }
@@ -987,8 +992,8 @@ video {
   padding-left: 0px;
 }
 
-.pl-2 {
-  padding-left: 0.5rem;
+.pl-\[260px\] {
+  padding-left: 260px;
 }
 
 .pr-6 {
@@ -999,14 +1004,6 @@ video {
   padding-top: 1.25rem;
 }
 
-.pl-\[250px\] {
-  padding-left: 250px;
-}
-
-.pl-\[260px\] {
-  padding-left: 260px;
-}
-
 .text-left {
   text-align: left;
 }
diff --git a/public/index.html b/public/index.html
index b45d452..357d296 100644
--- a/public/index.html
+++ b/public/index.html
@@ -21,7 +21,7 @@
       <template x-if="$store.app.currentPage === 'monitoring'">
         <main x-data="monitoringPage" class="flex-1" x-bind:hidden="$store.app.currentPage !== 'monitoring'">
           <div class="flex h-full flex-row space-x-2">
-            <div class="border-r fixed h-screen min-w-[256px] p-2.5 pl-0 pt-5">
+            <div class="border-r fixed bg-white h-screen min-w-[256px] p-2.5 pl-0 pt-5">
               <div class="flex flex-col space-y-1">
                 <!-- List of devices -->
                 <span class="italic text-sm">Devices:</span>
@@ -290,7 +290,12 @@
                             <h3 x-text="value.name" class="text-lg font-bold"></h3>
                             <div class="flex">
                               <!-- Edit display value -->
-                              <button>
+                              <button @click="$dispatch('open-display-value-modal', { 
+                                labels: { title: `Edit ${value.name}`, submit: 'Edit' },
+                                actionType: 'EDIT',
+                                selectedDevice,
+                                displayValue: value
+                               })">
                                 <svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24">
                                   <path
                                     fill="#eab308"
@@ -330,23 +335,27 @@
                       </template>
                       <!-- Create Display Value -->
                       <button
-                        @click="$dispatch('open-create-display-value-modal')"
+                        @click="$dispatch('open-display-value-modal', {
+                          labels: { title: 'Create new display value', submit: 'Create' },
+                          actionType: 'CREATE',
+                          selectedDevice,
+                        })"
                         class="flex justify-center min-h-[140px] items-center border-4 text-center border-dashed p-2.5 rounded-sm cursor-pointer hover:bg-gray-50"
                       >
                         <span class="text-5xl text-gray-400 font-bold select-none">+</span>
                       </button>
-                      <!-- MODAL: Create new display value -->
+                      <!-- MODAL: Display value -->
                       <template x-teleport="body">
                         <div
                           x-data="displayValueModal"
-                          @open-create-display-value-modal.window="open()"
+                          @open-display-value-modal.window="open($event)"
                           @keyup.escape.window="close()"
                           class="backdrop z-50"
                           x-show="isOpen"
                         >
                           <div class="modal">
                             <div class="flex justify-between items-center">
-                              <h2 class="font-bold text-lg">Create new display value</h2>
+                              <h2 x-text="labels.title" class="font-bold text-lg"></h2>
                               <button @click="close()" aria-label="Close">
                                 <svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24">
                                   <path
@@ -357,7 +366,7 @@
                               </button>
                             </div>
                             <hr />
-                            <form @submit.prevent="create(selectedDevice)" action="#">
+                            <form @submit.prevent="submit" action="#">
                               <div 
                                 x-id="['name', 'reg_addr', 'reg_type', 'reg_format']"
                                 class="flex flex-col space-y-2"
@@ -424,10 +433,10 @@
                                 <button
                                   x-bind:disabled="isLoading"
                                   x-bind:class="isLoading && 'opacity-70'"
+                                  x-text="labels.submit"
                                   type="submit"
                                   class="btn"
                                 >
-                                  Create
                                 </button>
                                 <button @click="close()" class="btn bg-red-500">Cancel</button>
                               </div>
diff --git a/public/js/app.js b/public/js/app.js
index 88b70ed..fc106d4 100644
--- a/public/js/app.js
+++ b/public/js/app.js
@@ -172,23 +172,44 @@ document.addEventListener("alpine:init", async () => {
       reg_type: 'IR',
       reg_format: 'UI16'
     },
+    labels: {
+      title: '',
+      submit: '',
+    },
+    selectedDevice: null,
     resetDataFields() {
       this.data.name = '';
       this.data.reg_addr = 0;
       this.data.reg_type = 'IR';
       this.data.reg_format = 'UI16';
     },
-    async create(selectedDevice) {
+    async create() {
+      this.isLoading = true;
+      const data = { ...this.data, slave_id: this.selectedDevice.id };
+      const result = await api.post('/modbus/create_display-value', data);
+      this.selectedDevice?.display_values?.push(result.data);
+      this.resetDataFields();
+      this.close();
+    },
+    async update() {
+      const data = { ...this.data, slave_id: this.selectedDevice.id };
+      await api.post('/modbus/update_display-value', data);
+      this.resetDataFields();
+      this.close();
+    },
+    async submit() {
       try {
         this.isLoading = true;
-        const data = {
-          ...this.data,
-          slave_id: selectedDevice.id
+        switch (this.actionType) {
+          case 'CREATE':
+            await this.create();
+            break;
+          case 'EDIT':
+            await this.update();
+            break;
+          default:
+            break;
         }
-        await api.post('/modbus/create_display-value', data);
-        selectedDevice?.display_values?.push(this.data);
-        this.resetDataFields();
-        this.close();
       } catch (error) {
         this.error = error;
         console.error(error);
@@ -196,8 +217,19 @@ document.addEventListener("alpine:init", async () => {
         this.isLoading = false;
       }
     },
-    open() {
+    open(event) {
+      const { labels, actionType, selectedDevice, displayValue } = event.detail
       this.isOpen = true;
+      this.labels = { title: labels.title, submit: labels.submit };
+      this.actionType = actionType;
+      this.selectedDevice = selectedDevice;
+      if (displayValue) {
+        this.data.id = displayValue.id;
+        this.data.name = displayValue.name;
+        this.data.reg_addr = displayValue.reg_addr;
+        this.data.reg_format = displayValue.reg_format;
+        this.data.reg_type = displayValue.reg_type;
+      }
     },
     close() {
       this.isOpen = false;
diff --git a/routes/api/modbus.router.js b/routes/api/modbus.router.js
index 9ebb288..8d4b36b 100644
--- a/routes/api/modbus.router.js
+++ b/routes/api/modbus.router.js
@@ -6,13 +6,18 @@ import { validateBodyMiddleware } from "#root/middlewares/index.js";
 const modbusRouter = express.Router();
 
 modbusRouter.get("/devices", modbusController.list);
+
 modbusRouter.post("/create_device", validateBodyMiddleware(modbusDeviceSchema), modbusController.createDevice)
 modbusRouter.post('/remove_device', validateBodyMiddleware(removeModbusDeviceSchema), modbusController.removeDevice);
 modbusRouter.post('/update_device', validateBodyMiddleware(modbusDeviceSchema), modbusController.updateDevice);
+
 modbusRouter.post('/create_display-value', validateBodyMiddleware(createDisplayValueSchema), modbusController.createDisplayValue);
+modbusRouter.post('/update_display-value', validateBodyMiddleware(displayValueSchema), modbusController.updateDisplayValue)
 modbusRouter.post('/remove_display-value', validateBodyMiddleware(removeDisplayValueSchema), modbusController.removeDisplayValue);
+
 modbusRouter.post("/connect", modbusController.connect);
 modbusRouter.post("/close", modbusController.close);
+
 modbusRouter.get("/data_stream", modbusController.streamData);
 modbusRouter.get('/status', modbusController.status);
 
diff --git a/validators/display-value.schema.js b/validators/display-value.schema.js
index 2230eb6..1078bdf 100644
--- a/validators/display-value.schema.js
+++ b/validators/display-value.schema.js
@@ -10,6 +10,4 @@ export const displayValueSchema = object({
 })
 
 export const removeDisplayValueSchema = displayValueSchema.pick(['id']);
-
-// TODO: "reg_format" can be BOOL if "reg_type" is "DI" or "DO"
 export const createDisplayValueSchema = displayValueSchema.omit(['id'])
\ No newline at end of file