Field value greater than previous record
I have a layout with a portal in. In this portal I have a drop down list to select a certain piece of equipment. I then enter a field value for this equipment, total running hours. Every week I'll be creating a new record and entering the new total running hours for this equipment, so how do I ensure that the most recent value entered will be greater than from the previous record. The records are linked by a vessel name and each record has an ID number associated with it.
Also I need to take into account the fact the first entry/record will not have a previous record to compare to.
I'm not sure how to go about this. Can anyone help me with this? Thanks.