Correction factor for HV probes?

[Scott_L_Hanson-at-notes.seagate-dot-com (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Soliciting input from anyone on the Tesla List on the following:

Many older high voltage probes are available on the used equipment market.
Most of these were originally calibrated for use with meters with 100k Ohm
or 1 meg Ohm input impedence.

What type of correction or compensation (if any) is required when these
probes are used with modern digital multimeters having 10 meg Ohm input
impedence?

What's the magnitude of the error expected without any compensation?

Regards,
Scott