The precision of the compact Mini-Accelograph (M-A) was compared with the Myograph 2000 (MYO). Neuromuscular block resulting from atracurium was measured simultaneously by the MYO and the M-A applied to contralateral thumbs. During onset, the M-A frequently underestimated the extent of block (maximal at approximately 50% twitch depression). The M-A control train-of-four (TOF) ratio was characteristically > 1.0 and remained greater than the MYO ratio during the onset of atracurium. During recovery, the difference between the MYO and the M-A was maximal at approximately 50% twitch depression, but the M-A frequently overestimated the extent of block. The mean differences between the MYO and the M-A were small in respect of the recovery index (RI) and the TOF. However, the limits of agreement were unacceptably wide for both TOF and RI. When the MYO TOF was 0.7, the corresponding M-A TOF varied between 0.4 and 1.0. The M-A was more susceptible to drift than the MYO.