Hi Herman,<br>
<br>
The DC differential impedance is 100 kOhm. The AC differential impedance is frequency dependent and given on page 28 of the <a href="https://www.tek.com/en/p7513-manual/p7500-series-rev">technical reference</a>.<br>
<br>
As you can see, the AC impedance is more than 50 Ohms (in the rated bandwidth) but not as high as the DC impedance, but it is high enough that the tip can be used mid-bus and is, therefore, a "high impedance" probe tip in a relative term.