A tiny circular ruler. Rollbe is perfect for taking short measurements, whether straight or curved. It’s available in two sizes: 4″/10cm and 8″/20cm. It would’ve been neat if it made a sound or had a larger knurl to indicate a full rotation.
Crowdfunded projects pose a degree of risk for buyers, so be sure to do your research and fully read the seller's detailed description and production plans before plunking down your hard-earned money.