| 摘要 |
Each of the discs (1-4) has a first group of segments (11) in which each segment field (13) has a symbol, and a second group of segments (10) in which each segment field (15) lacks a symbol and can be easily provided with a marking, e.g. by providing it with a surface for marking the symbol on. The number of segment fields in the second group is greater than that in the first group. |
