The sapphire SI-9000 is a active differential probe with a bandwidth from DC to 25MHz and switchable attenuation of 1:10 and 1:100 for voltages up to 70/700Vrms. The SI-90000 is an older model, manufactured completely in throughhole technology. I bought it relatively cheap over ebay Kleinanzeigen. My probe is in a very good shape of preservation, almost as new.