> ## Documentation Index > Fetch the complete documentation index at: https://docs.getmelody.io/llms.txt > Use this file to discover all available pages before exploring further. # Retrieve Server Time > # Retrieve Server Time in milliseconds ## **Guide for Server Time Synchronization (Using EWMA)** To ensure accurate synchronization with the server time, follow these steps: 1. Call the API endpoint /device/server-time multiple times and get server time in ms(**epoch_ms**). A higher number of requests improves accuracy but increases synchronization time. At least 10 times could be a good start. 2. For each request, note the time when the request is sent (**sent_at**) and when the response is received (**received_at**). 3. Calculate RTD (Round Trip Delay): **RTD** = **received_at** - **sent_at**. 4. Adjust for network delay by adding half of RTD to the received server time: **server_time_estimated** = **epoch_ms** + **RTD** / 2 5. Calculate the time difference between the **server_time_estimated** and the client’s current time (**client_ts**): **time_diff** = **server_time_estimated** - **client_ts**. 6. Instead of a simple average, use Exponentially Weighted Moving Average (EWMA) to smooth out variations: ``` alpha = 0.3 # Smoothing factor, 0.1 to 0.3 (recommended for balancing stability and responsiveness). ewma = alpha * time_diff + (1 - alpha) * ewma ``` 7. Use the EWMA-adjusted offset to compute the synchronized server time when sending data: ``` synchronized_server_time_ms = client_ts + ewma ``` 8. Use the synchronized server time to send data to the device in the corresponding API endpoints. ## OpenAPI ````yaml /api-reference/openapi_sdk.yaml get /device/server-time openapi: 3.1.0 info: title: Haptics SDK API contact: name: Haptics API Support email: support@getmelody.io url: https://docs.getmelody.io/spec description: > # Introduction Welcome to the Haptics Docs API! You can use our API to access Haptics SDK endpoints. All API requests must contain header `Content-Type: application/json` by default. If not explicitly specified otherwise. Haptics Prod: [api.getmelody.io](https://api.getmelody.io) Haptics Stage: [api.haptics.devlikereal.com](https://api.haptics.devlikereal.com) # Authentication Access is scoped to your **organization**. Your **Organization ID** and **Developer Key** (Melody Key) are issued to you by Melody — contact [support@getmelody.io](mailto:support@getmelody.io) to request them. To call device endpoints: 1. Link a device to your organization with `POST /device/otp/confirm/v2` (send your Developer Key in the `X-Org-Key` header) to obtain its **Device Key**. 2. Exchange your Developer Key for a short-lived **session token** with `POST /api/sessions/v2`. 3. Call any `/device/*` endpoint with `Authorization: Bearer ` and the `X-Device-Key: ` header. version: v4 servers: - url: https://api.getmelody.io description: Production - url: https://api.haptics.devlikereal.com description: Staging security: [] tags: - name: Authentication description: > Obtain and use organization-scoped access tokens. Your Organization ID and Developer Key (Melody Key) are issued to you by Melody — contact support@getmelody.io to request them. - name: Device Information description: | The Device Information API encompasses two primary functionalities: This section includes endpoints that enable you to: - Retrieve detailed information about the device. - Access information related to the current session. - Update device settings efficiently. - Set required device mode. - name: Haptic Direct Control description: > Section convers Direct Control mode. User is able to set position & time to get the receiver there. - name: Haptic Points Stream description: > Section covers Points Stream mode. Mode for streaming arrays of signal with device position & signal time in the original sender’s timescale. The stroker movement velocity is calculated on device and is based on time difference between signals. At least two signals needed to calculate stroker velocity & move the stroker. - name: Haptic Script Control description: > Section covers Script Playback. The script is sent to device by passing the link. After script downloaded by device, server controls device with start, stop, pause commands. - name: Haptic Loop Control description: > Section covers Loop Playback. Mode for simple up/down stroking without the need for data points. It only needs stroker velocity percentage and min/max positions for stroking range to create a loop and move according provided range. - name: One-Time Password description: > Section covers One-Time Password. The one-time password is valid for 10-15 minutes, required for device bootstrapping with 3rd party services. - name: Maintenance description: > This section provides APIs dedicated to the upkeep and troubleshooting of the device. Key functionalities include: - Firmware Updates: APIs to check for, download, and apply firmware updates, ensuring the device is running the latest software version with improved features and fixes. - Debug Information: Access detailed diagnostic data and logs to facilitate troubleshooting and performance analysis. - Debug Logging: Enable or disable real-time debug log emission from the device. When enabled, the device sends unsolicited `DEBUG_LOG` frames (frame type `21`) over the WebSocket. Each frame carries a `DebugLogMessage` protobuf payload with a single `message` string field. Logs are stored server-side per device (up to 1000 entries) and can be viewed in the CMS device detail page. paths: /device/server-time: get: tags: - Device Information summary: Retrieve Server Time description: > # Retrieve Server Time in milliseconds ## **Guide for Server Time Synchronization (Using EWMA)** To ensure accurate synchronization with the server time, follow these steps: 1. Call the API endpoint /device/server-time multiple times and get server time in ms(**epoch_ms**). A higher number of requests improves accuracy but increases synchronization time. At least 10 times could be a good start. 2. For each request, note the time when the request is sent (**sent_at**) and when the response is received (**received_at**). 3. Calculate RTD (Round Trip Delay): **RTD** = **received_at** - **sent_at**. 4. Adjust for network delay by adding half of RTD to the received server time: **server_time_estimated** = **epoch_ms** + **RTD** / 2 5. Calculate the time difference between the **server_time_estimated** and the client’s current time (**client_ts**): **time_diff** = **server_time_estimated** - **client_ts**. 6. Instead of a simple average, use Exponentially Weighted Moving Average (EWMA) to smooth out variations: ``` alpha = 0.3 # Smoothing factor, 0.1 to 0.3 (recommended for balancing stability and responsiveness). ewma = alpha * time_diff + (1 - alpha) * ewma ``` 7. Use the EWMA-adjusted offset to compute the synchronized server time when sending data: ``` synchronized_server_time_ms = client_ts + ewma ``` 8. Use the synchronized server time to send data to the device in the corresponding API endpoints. operationId: get-device-server-time parameters: - $ref: '#/components/parameters/XDeviceKey' responses: '200': description: OK content: application/json: schema: type: object properties: epoch_ms: type: integer format: int64 description: The current server time in milliseconds. security: - SessionToken: [] components: parameters: XDeviceKey: name: X-Device-Key in: header required: true description: | Device Key (4 BIP39 words) identifying the target device. Obtain it from `POST /device/otp/confirm/v2`. schema: type: string pattern: ^[a-z]+-[a-z]+-[a-z]+-[a-z]+$ example: alpha-bravo-charlie-delta securitySchemes: SessionToken: type: http scheme: bearer description: > Short-lived session token obtained from POST /api/sessions/v2. Send it as `Authorization: Bearer ` together with the `X-Device-Key: ` header identifying the target device. ````