Glossary for detailled explanation - take your pick:
If it is required to execute a measurement at a certain point in the process, the transmission and reception can be interrupted by connecting the hold input with GND. Then, the last calculated distance value is saved and released. After reactivating the sensor, a new distance value is released after one measurement cycle. To activate the hold function, a switch or NPN open collector output can be used. By linking the hold inputs with each other, the function of several sensors is synchronised in the most simple way.