point will be detected and and recorded as tp 2 the signal then becomes of lower amplitude and passes below the range level 7 to tp 3 at which a turning point is detected and recorded although of course the digital value will be 7 the signal then rises to tp 4 and then proceeds downwardly passing through a level shown at x which corresponds to the penultimate recorded turning point level tp 3 the range levels at tp 3 and tp 4 are extracted from the lifo memory this then leaves the range value at tp 2 the last value in the memory and indeed leaves tp 1 as the one before last value or the penultimate value it will be seen that as the signal then proceeds downwardly to tp 5 once again equality in level will be detected at range level 3 and the range levels at tp 2 and tp 1 will be extracted from the memory and stored perhaps more importantly now there will be recorded a time associated with tp 3 and tp 4 and a differential time shown as 12 which will in fact identify a characteristic of the signal referred to as a domain value likewise upon the range.