ClockZero

Clean clock calibration and device time offset checker.

In production, this application is deployed as a single project on Vercel containing both static files and Vercel Serverless Functions.

Project Structure

clockzero/
├─ api/    # Vercel Serverless Functions (/api/sync, /api/time, /api/health)
├─ public/ # Static assets
├─ src/    # Frontend React source code
│  └─ lib/
│     └─ shared.ts # Shared types and utilities
├─ index.html
├─ package.json
├─ tsconfig.json
├─ vite.config.ts
└─ README.md

Install

Run from root:

pnpm install

Dev

Run Vite dev server:

pnpm dev

Or run Vercel CLI dev server to test functions locally:

pnpm dev:vercel

Build & Typecheck

pnpm typecheck
pnpm build

Endpoints

• GET /api/health - Basic service health
• GET /api/time - Current server system time
• GET /api/sync - Server system time with calibration metadata

Vercel Deployment

Deploy this repository directly to Vercel with default settings:

• Root Directory: ./ (default)
• Framework Preset: Vite
• Build Command: pnpm build
• Output Directory: dist
• Install Command: pnpm install

Time Synchronization Formula

The client records and calculates offsets using Round-Trip Time (RTT):

const t0 = performance.now();
const local0 = Date.now();

const res = await fetch("/api/sync", { cache: "no-store" });
const data = await res.json();

const t3 = performance.now();

const rtt = t3 - t0;
const estimatedServerAtReceive = data.serverUnixMs + rtt / 2;
const estimatedLocalAtReceive = local0 + (t3 - t0);
const offsetMs = estimatedServerAtReceive - estimatedLocalAtReceive;
const estimatedAccuracyMs = rtt / 2;

Accuracy Disclaimer

Browser clock accuracy depends on:

• Network RTT and jitter
• CPU scheduling and rendering frame rates (requestAnimationFrame/setInterval limits)
• Host OS clock synchronization on the server side