Help with calculating a sum of lengths for a specific grouping of records within a database
I cannot figure out how to calcuate a total_length field that can be stored so I can use it in another calculations.
I need to find a percentage of something within a length of transect I walked. The transect is broken into multiple units. Each unit has its own number and date. There are multiple records in my database with different units/dates, but I need to calculate a stored data field for the entire unit length of my individual transects so I can determine the total percentage of substrates, etc, along only that transect- not others.
The first thing I tried to do was when I created the cumulative length field, I clicked "summary" and then "fraction of the total of." The issue is that I am only allowed to click one subtotal field to link those records to my particular result. I really need to click two fields (date AND unit name) to make the database pull the correct records to be totaled.
How do I do this??? Thanks so much.