The measurement of negative gauge pressure is a field of increasing importance in science and industry. One of the main aims of the EMPIR Joint Research Project 14IND 06 pres2vac is to develop guidelines for it. We present a comparison of three different methods for measuring negative gauge pressure: (i) using two absolute pressure measuring instruments, (ii) generating a negative gauge pressure in the bell jar of the pressure balance, and (iii) using a 'hanging piston' pressure balance. The advantages and drawbacks are discussed and some preliminary results presented.