You would set up the relation in the new mileage intervals table. Relations look for matching values, so when you create your relation column, you will select your interval column, then match it up to the interval column in your existing log table. Also, make sure you have selected the Multiple checkbox when setting up the relation. You want to do that because you are matching one row in your mileage table to many rows in your log table.
If you are getting matches, then the relation is working. You just have to keep in mind that relations return rows. Not any specific column. You may be seeing the mileage in the relation column, but that’s just telling you that it found a match. What it shows is irrelevant.
Now that you have your relation set up, you would create a tab in your app that points to your mileage table. This will give you a list of each mileage. When you click on it, you will get a detail screen for that mileage row. Here is where you can add an inline list that uses the relation column as the source. This will then show all of the related matching log entries for the mileage interval you are viewing.