DETAILED DESCRIPTION The present invention provides a holographic data verification system which is capable of simultaneously verifying numbers, as the term is defined above, belonging to one or more number systems, e.
g.
belonging to several types of credit cards.
Thus, the present invention provides a readily accessible memory which may store any desired number of "number systems".
As used herein, the terms "number system" or "number type" denote a set of number which may, for example, be the cards issued by a given airline, or the identity of persons within a group of persons, say within the military or within a military service, and the like.
Consequently, each number system includes an identifying symbol for the numbers which belong to it, and any given number may be duplicated in two or more such systems, which, therefore, might only be distinguishable by their identifying symbol.
The present invention also records the holograms of the memory in a plurality of parallel elongate hologram rows or channels.
In contrast to the prior art, however, and to minimize access times and the length of film required by the memory the channels are of "substantially equal length".
As used herein, the term "substantially equal length" is intended to mean and means lengths which are approximately the same although they may vary slightly but insignificantly; and further the term means that at least one channel may be of a significantly shorter length in case the memory includes an insufficient number of holograms to fill all channels.
Since it cannot be predicted in advance how many numbers from each number system will be recorded in the memory, and since the hologram channels of the memory are of substantially equal length, it is not possible to assign in advance one or more channels to any number system.
Instead, in accordance with the present invention, the numbers in each number system and the number groups themselves are sequentially recorded.
To avoid the need for scanning all hologram channels for a given number an index for the memory is provided
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Optical Systems 
