The Agilent 1158A active probe offer R & D engineers the performance they need to probe small geometries in hard to reach areas on the DUT. These probe were designed specifically for the Infiniium Series oscilloscopes. As the speeds in your design increase, you may notice more overshoot, ringing, and other anomalies when connecting an oscilloscope probe. Probes form a resonant circuit where they connect to the device. If this resonance is within the bandwidth of the oscilloscope probe you are using, it will be difficult to determine if the measurement anomalies are due to your circuit or the probe.