Update record in related table

I have two tables, Samples and Locations. The user will go out and create new samples at the same locations each month. When they choose a location in the sample table, I'd like a field ( ex. pressure reading) in the sample to display the pressure reading from the location that was selected. If duing that month's sampling the pressure changes, the user should be able to update the pressure field from the location table with data entered in the sample table. 

Hopefully this makes sense. 

Thanks for any help!