jgg     2014 34 (6):  180-182    ISSN: 0412-1961  CN: 21-1139/TG STUDY ON INDOOR VERIFICATION METHOD OF DIGITAL LEVEL First Crust Monitoring and Application Center,CEA，Tianjin 300180 Received: 2014-07-09  Revised: null  Online: 2014-12-09 Supporting info