CrystalReprot question

I have database with two tables. In first table I have 2 fields; DEBT and DEMAND.
In second table I have one field with some number value, let's name it VALUE with
value 1000.

My task is to make report like this:

DEBT DEMAND BALANCE
100 0 1100
200 0 1300
0 100 1200

I have created formulafield BALANCE with next code:

whileprintingrecords;
({FirstTable.DEBT} - {FirstTable.DEMAND}) + {SecondTable.VALUE};

After running report I get next result:

DEBT DEMNAD BALANCE
100 0 1100
200 0 1200
0 100 900

which is not correct...

Can somebody help me with that? My head will blow... ((
Thnx.

J.