Table 1
Backbones used in this study.
| Backbone | Id | Period of observations | Observers | Nd | Mda | ||
| series | primary observer | ||||||
|
|
|||||||
| RGO | 332 | 1882–2010 | 1900–1976 | 81 | 46 087 | ||
| Kanzelhöhe | 606 | 1935–2010 | 1957–2010 | 156 | 25 690 | 25 526 | |
| Wolfer | 335+338 | 1858–1935 | 1876–1928 | 25 | 22 968 | 16 601 | |
| Schmidt | 292 | 1841–1900 | 1841–1883 | 11 | 18 240 | 11 708 | |
| Schwabe | 279 | 1822–1892 | 1825–1867 | 22 | 14 160 | 7386 | |
| Flaugergues | 22+227 | 1774–1844 | 1788–1830 | 12 | 6948 | 1383 (1503) | |
| Horrebow | 180 | 1749–1799 | 1761–1776 | 4 | 2762 | 1775 (1795) | |
| Schubert | 178 | 1754–1758 | 1754–1758 | 1 | 492 | 10 (20) | |
| Zucconi | 177 | 1754–1760 | 1754–1760 | 1 | 899 | 17 (29) | |
| Hagen | 161 | 1739–1751 | 1739–1751 | 1 | 116 | 21 (34) | |
Notes. Columns are: name and identification (Id) of the primary BB observer; period covered by the BB composite series; period of observations of the primary observer; number of observers included in the BB series; number Nd of daily observations of the BB composite series; and direct daily overlap with the reference BB series, i.e. the number of days available in both BB series Md.
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