1. The baseline difference between different theodolites Xin Changjiang Lanzhou Observatory, Lanzhou Institute of Seismology, China Earthquake Administration Abstract Some observatories have been installed two theodolites in China since 2008, so they got two independent baselines for one fluxgate variameter. We supposed the two baselines should keep same change in the beginning, but we found most observatories shown two baselines did not coincide in some degree after operating more than one year. The following graphs show the above facts: variameter-M15 made in Danmark, DB component, red for MINGEO theodolite made in Hungary, blue for MAG2KP made in Hungary Lanzhou Observatory variameter-M15 made in Danmark, DB component, red for CTM theodolite made in China, blue for MINGEO made in Hungary Kashi Observatory variameter-GM4 made in China, DB component, blue for CTM theodolite made in China, red for MINGEO made in Hungary Qianling Observatory variameter-M15 made in Danmark, DB component, blue for CTM theodolite made in China, red for MINGEO made in Hungary Qianling Observatory variameter-M15 made in Danmark, DB component, red for CTM theodolite made in China, blue for MINGEO made in Hungary Changchun Observatory variameter-M15 made in Danmark, DB component, red for CTM theodolite made in China, blue for MINGEO made in Hungary Chengdu Observatory variameter-M15 made in Danmark, DB component, blue for CTM theodolite made in China, red for MINGEO made in Hungary Wuhan Observatory variameter-M15 made in Danmark, DB component, blue for CTM theodolite made in China, red for MINGEO made in Hungary Wulumuqi Observatory variameter-M15 made in Danmark, DB component, blue for CTM theodolite made in China, red for MINGEO made in Hungary Dedu Observatory variameter-GM4 made in Danmark, DB component, blue for CTM theodolite made in China, red for MINGEO made in Hungary Mengcheng Observatory DB: HB: variameter-M15 made in Danmark, HB component, red for MINGEO theodolite (D 、 I) made in Hungary, blue for MAG2KP (D 、 I) made in Hungary, GSM magnetometer (F) made in Canada Lanzhou Observatory variameter-M15 made in Danmark, HB component, red for CTM theodolite (D 、 I) made in Hungary, blue for MINGEO (D 、 I) made in Hungary, GSM magnetometer (F) made in Canada Kashi Observatory variameter-GM4 made in China, HB component, blue for CTM theodolite (D 、 I) made in China, red for MINGEO (D 、 I) made in Hungary, GSM magnetometer (F) made in Canada Qianling Observatory variameter-M15 made in Danmark, HB component, blue for CTM theodolite (D 、 I) made in China, red for MINGEO (D 、 I) made in Hungary, GSM magnetometer (F) made in Canada Qianling Observatory variameter-M15 made in Danmark, HB component, red for CTM theodolite (D 、 I) made in China, blue for MINGEO (D 、 I) made in Hungary, GSM magnetometer (F) made in Canada Changchun Observatory variameter-M15 made in Danmark, HB component, red for CTM theodolite (D 、 I) made in China, blue for MINGEO (D 、 I) made in Hungary, GSM magnetometer (F) made in Canada Chengdu Observatory variameter-M15 made in Danmark, HB component, blue for CTM theodolite (D 、 I) made in China, red for MINGEO (D 、 I) made in Hungary, GSM magnetometer (F) made in Canada Wuhan Observatory variameter-M15 made in Danmark, HB component, blue for CTM theodolite (D 、 I) made in China, red for MINGEO (D 、 I) made in Hungary, GSM magnetometer (F) made in Canada Wulumuqi Observatory variameter-M15 made in Danmark, HB component, blue for CTM theodolite (D 、 I) made in China, red for MINGEO (D 、 I) made in Hungary, GSM magnetometer (F) made in Canada Dedu Observatory ZB: variameter-M15 made in Danmark, ZB component, red for MINGEO theodolite (D 、 I) made in Hungary, blue for MAG2KP (D 、 I) made in Hungary, GSM magnetometer (F) made in Canada Lanzhou Observatory variameter-M15 made in Danmark, ZB component, red for CTM theodolite (D 、 I) made in Hungary, blue for MINGEO (D 、 I) made in Hungary, GSM magnetometer (F) made in Canada Kashi Observatory variameter-GM4 made in China, ZB component, blue for CTM theodolite (D 、 I) made in China, red for MINGEO (D 、 I) made in Hungary, GSM magnetometer (F) made in Canada Qianling Observatory variameter-M15 made in Danmark, ZB component, blue for CTM theodolite (D 、 I) made in China, red for MINGEO (D 、 I) made in Hungary, GSM magnetometer (F) made in Canada Qianling Observatory variameter-M15 made in Danmark, ZB component, red for CTM theodolite (D 、 I) made in China, blue for MINGEO (D 、 I) made in Hungary, GSM magnetometer (F) made in Canada Changchun Observatory variameter-M15 made in Danmark, ZB component, red for CTM theodolite (D 、 I) made in China, blue for MINGEO (D 、 I) made in Hungary, GSM magnetometer (F) made in Canada Chengdu Observatory variameter-M15 made in Danmark, ZB component, blue for CTM theodolite (D 、 I) made in China, red for MINGEO (D 、 I) made in Hungary, GSM magnetometer (F) made in Canada Wuhan Observatory variameter-M15 made in Danmark, ZB component, blue for CTM theodolite (D 、 I) made in China, red for MINGEO (D 、 I) made in Hungary, GSM magnetometer (F) made in Canada Wulumuqi Observatory did not coincide perfectly in most observatories. Some baselines had difference in trend. Some existed inconsistent in some period. Especially the problem appeared in DB component. This problem meant the different theodolites produced different datum at the same observatory. Thanks Pro. Yang, s group for providing baseline data. Questions: On the base of above graphs, we observed two baselines measured by two theodolites for same component of a variameter in 2009