High values of fixed cross-fault leveling appeared simultaneously in Feng Jiafang and Xiang Gongzhuang in Yishu fault-zone when precision levelers were replaced by DiNill-type digital ones.By utilizing the observation data from Feng Jiafang and Xiang Gongzhuang leveling from Jan. to July in 2000

2001 and 2002

Analysis shows that the observation precisions by using precise and digital levers are different. The latter’s precision is lower than that of the former. With 0. 05 confidence level

t- and f-test indicate that both mean and mean-square-error of observation by using these two-type levelers in same periods of several years are obviously different. It seems that the high values appeared are mainly conccrnd in instruments change in Feng Jiafang and Xiang Gongzhuang stations

and the variation of natural circumstance such as rainfall

air temperature etc. are also possible effecting factors. High values appeared in Feng Jiafang leveling station are related to the change of air temperature and underground water level with complex-correlation coefficient of 0. 67. In Xiang Gongzhuang leveling station

interference of circumstance nearby

such as the dewatering caused by irrigation-well near the observation station

was the im portant cause of deformation of the East/South common point.