Step 1 - the starting value of specific gifts: legal rights in Scotland
IHTA84/S42 (4) governs the value of legal rights (IHTM12221) in Scotland claimed by a person entitled to claim them.
The legal rights claimed must be treated as a specific gift (IHTM26011) which bears its own tax (IHTM26003) when applying the partly exempt transfer rules (IHTM26071). When valuing such legal rights you should leave out of account any tax payable on the death of the deceased.
You should also see the instructions on the burden of tax (IHTM26201)