H. J. Choi, K.H. Gil, H.-S. Kang, S.H. Kim, and K.W. Seo,
   "The BINP HLS to Measure Vertical Changes on PAL-XFEL Buildings and Ground",
   in Proc. 37th International Free Electron Laser Conference, Daejeon, Republic of Korea, August 2015, paper MOP047, pp. 133-135,
    ISBN: 978-3-95450-134-2,
    doi:10.18429/JACoW-FEL2015-MOP047,
    http://accelconf.web.cern.ch/AccelConf/FEL2015/papers/mop047.pdf, 2015.