Tahometer 3.5.2 for Windows is out. It’s a small release focused on two things you told us about.
Screenshots of your second monitor are back. Since 3.5.1, screenshots of any monitor other than the main one came out solid black. 3.5.2 captures every monitor correctly again.
Updates finish reliably. If Tahometer started automatically with Windows, clicking Update could close the app without updating, and it wouldn’t come back on its own. Updates now complete no matter how Tahometer was started. If an update fails for any reason, Tahometer reopens with a short note and offers the update again later, so tracking never quietly stops.
How to get it: Tahometer will offer the update on its own. If you click Update and the app closes without updating, quit Tahometer from the tray icon, reopen it from the Start menu, and accept the update. You only need to do this once. You can also download the installer directly.