You should be able to accomplish this using a combination of parameters and calculated fields.
The first step is to create two parameters, one that corresponds to the Start Date of the date range and one that corresponds to the End Date of the date range. When you create each of these Parameters, make them a Date list and then Add from the Reading Date field. You can adjust the display of these parameters so that they are sliders or drop down menus.
The next step is to create calculations that pull out the Odometer readings at the Start Date and End Date:
IF [Reading Date] = [Start Date] THEN [Odometer] END
* duplicate and use [End Date] for the second calculation
Finally, create the Delta calculation to compare these two values:
SUM([End Date Odometer]) - SUM([Start Date Odometer])
I've attached a workbook that demonstrates how this solution can be implemented. The correct Delta value is calculated at the Vehicle ID level, this means that bringing additional fields onto the view (ex: Reading Date) could affect the values. The bar chart in the attached workbook reflects the correct values. This solution requires two sliders because the starting and ending date must be independent variables that correspond to separate calculated fields.
Hope this helps!
223104_forum_response.twbx 16.0 KB