This tool calculates the overall combined bandwidth of an oscilloscope and probe used to make the measurement. It also provides the minimum rise time of the input signal.
The bandwidth of the probe used with an oscilloscope impacts the effective bandwidth. The picture below (from Tek) shows how this can can impact a measurement. The waveform appears distorted due to inadequate bandwidth.
The calculator on this page calculates the effective system bandwidth.
System Bandwidth = 1/√(1/BandwidthPROBE2 + 1/BandwidthOSC2)
Rise time = 0.35/(System Bandwidth)
Using a 50 MHz probe with a 100 MHz bandwidth oscilloscope gives a system bandwidth of about 45 MHz. This gives a minimum rise time of 7.8 ns. If the rise time of the input signal is smaller, it will result in an erroneous measurement.
If instead a 200 MHz probe was used, the system bandwidth is 89 MHz. It takes a 500 MHz probe to get a system bandwidth of 98 MHz.
Rise Time – Use the oscilloscope bandwidth to determine the minimum rise time that can be measured. In general the higher the scope bandwidth, the lower the rise time.