since the tables are linked, and table2 has 4 lines, then it would print the value from table1 4 times. Think of it as SQL select (if you know SQL) and it should help.
So, it you want a count of table2, that's easy, but if you want a count of table1, you want to use DistinctCount. If you are looking for a SUM of table1, for simplicity, I would SUM the value and then DIVIDE by the COUNT, like:
SUM({table.field}, {group})/COUNT({table.field}, {group})
why? since the sum of the table1 is being inflated by 4 times (since there are 4 rows) divide by 4 to remove the inflation.
HTH