I have had to split one automation rule into two because the rule runs so fast that the two fields we want updated do not both get updated when the rule is in one. The first part of the rule executes and the mathematical calculation happens and the value is stored in the first field, but the second part, where we update the second field with a corresponding value based on the calculation is not getting done.
So we are attempting to have the first part of the process placed in one rule and have that call a second rule. We have split the logic, checked that both rules can be called by other rules, they are both global rules and.... now what? I do not see anything under actions that says, "Call a rule."