A location-trace comparison system can perform privacy-preserving computations on locations traces for two or more users, for example, to determine a location-visit overlap for these users. The protective ring thus formed, which is characterized by tough-elastic properties and low weight, can be used as a full containment with sufficiently large wall thickness or as a penetration containment with smaller wall thickness and with a trapping layer arranged on the outer circumference. The fiber quality measurement instrument is connected through a communications network, such as the internet, for uploading fiber quality data to a database storage device. A die-cast machine is also disclosed.