Using this product is easy. To use the stopwatch, just press the start button to begin timing. You can record up to 25 sets of stopwatch data. For tire pressure checks, turn the gauge on and attach it to the tire valve. It will show the pressure in either PSI or BAR. You can measure temperature too, which is shown in Fahrenheit or Celsius. Remember to keep the gauge clean and dry. Don't drop it or expose it to extreme temperatures. When not in use, store it in a safe place. If you want to save tire pressure data, make sure to switch to the appropriate mode. And when timing multiple drivers, ensure you set the correct number of drivers and split times. This way, you'll get the most out of your Prisma HPM4X-STW gauge.