batch 1 – 3 bolts of 5 left (5-2=3 – correct)
batch 2 – 4 bolts of 6 left (6-4=2 – incorrect, should be 2 bolts of 6 not 4)
Text in red shows the correct calculation and results, not the incorrect results. Did you mean to say that the second calculation works out as:
6 - 2 = 4? for a total of 7?
You seem to have a correct analysis of why you are getting an incorrect total--the relationship matches to the wrong record and thus you get the wrong calculation results.
But there's no where near enough information about your tables and relationships to be able to suggest a solution in any kind of detail. Best guess from the description is that you are using one relationship between a pair of tables where you need two different relationships matching by different combinations of match fields so that both parts of your system compute correct results. This can be done by adding additional Tutorial: What are Table Occurrences? in order to get more than one relationship between the same two tables.
Yes I explained a little badly, I'm not bending maths I know that 6-4=2 is correct. Yes what I meant to say was that the second calculation works out as 6-2=4 giving me total of 7 which is incorrect.
I'll look into your table occurrences tutorial and give it another try. If that doesn't help then I'll provide you with more detailed information about my tables and relationships.