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Four clusters with years
| Machine | Human | Buddy | Infrastructure | Total | |
|---|---|---|---|---|---|
| 1912–1945 | 3 | 7 | 2 | 0 | 12 |
| 1946–1995 | 9 | 32 | 19 | 14 | 74 |
| 1996–2019 | 6 | 7 | 5 | 11 | 29 |
| Total | 18 | 46 | 26 | 25 | 115 |
| Average |
1977.5 SD 29.2 |
1979.3 SD 21.9 |
1981.4 SD 21.8 |
1994 SD 18.0 |
1981.1 SD 27.0 |
