Ticket# 3534420
Example:
  • Opportunity Value =
    $1,000
  • Opp Custom Field for Commission Percent =
    10
  • Opp Custom Filed for Commission Owed =
    $100
Right now, the Opportunity's custom fields
can be used as inputs
but not UPDATED via the Math action.
Of course, please do it for all Object types, not just Opportunities.