This paper discusses the use of distributed instruments for performance evaluation of Real-Time Ethernet (RTE) networks. A new instrument, composed of several logging probes connected in different points of a RTE target network, is characterized and compared with commercially available test equipments. The most important problem in performance evaluation is the timestamp assignment to network events; special attention has been paid in measuring synchronization uncertainty among probes. In fact, experimental results show a synchronization accuracy less than 150 ns on timestamp assignments among probes of the same instrument. In the last part of the paper, a sample application on a real network has been described, illustrating the use of the proposed instrument.