The six things a rule controls
Start with the simplest setting that does the job. A condition reads as a sentence in the builder. Use an expression only for what a condition can’t say.
Every one of these can read the object a record links to. See Rules that read a linked object.
Guides
Link fields
Link a record to another object, or to a list of objects.
Rules on linked objects
Show, require, lock, check or fill a field from a linked object.
Lock a field
Make a field read-only always, or while a rule is true.
Options by location
Offer only the dropdown options that apply where the crew is.