The work presents the results of surveying and analysing of the levelling line that was used in 1997 for connecting fundamental national height networks of the geometric levelling established in the Republic Hungary and the Republic Croatia. The levelling line was double surveyed that has been done mutually independently using digital and classical levelling instruments and appropriate accessories. The survey of levelling line was repeated because of lack of experience in working with modern digital instruments for the purpose of obtaining high accuracy geometric levelling.