latter is stopped and all leftover flip-flops are sampled opaque. Analogous to the above case of the oscillators the wanted time interval is then with n the number of cells marked as transparent. Tapped delay line In general a tapped delay line contains a number of cells with well defined delay times . Propagating through this line the start signal is delayed. The state of the line is sampled at the time of the arrival of the stop signal. This can be realized for example with a line of D-flip-flop cells with a delay time . The start signal propagates through this line of transparent flip-flops and is delayed by a certain number of them. The output of each flip-flop is sampled on the fly. The stop signal latches all flip-flops while propagating through its channel undelayed and the start signal cannot propagate further. Now the time interval between start and stop signal is proportional to the number of flip-flops that were sampled as transparent. Hybrid measurement Counters can measure long intervals but have limited resolution. Interpolators have high resolution but they cannot measure long intervals. A hybrid approach can achieve both long intervals and high resolution. The long interval can be measured with a counter. The counter information is supplemented with two time interpolators: one interpolator measures the (short) interval between the start event and a following clock event, and the second interpolator measure the interval between the stop event and a following clock event. The basic idea has some complications: the start and stop events are asynchronous, and one or both might happen close to a clock pulse. The counter and interpolators must agree on matching the start and end clock events. To accomplish that goal, synchronizers are used. The common hybrid approach is the Nutt method. In this example the fine measurement circuit measures the time between start and stop pulse and the respective second nearest clock pulse of the coarse counter (Tstart, Tstop), detected by the synchronizer (see figure). Thus the wanted time interval is with n the number of counter clock pulses and T0 the period of the coarse counter. History Time measurement has played a crucial role in the understanding of nature from the earliest times. Starting with sun, sand or water driven clocks we are able to use clocks today, based on the most precise caesium resonators. The first direct predecessor of a