Why is my table sometimes updated with Wrong Value in a multi-user environment?
But if I run a sequential update program the result is right.

Table 1: (Currency Master Table)
fieldname: CURR1, BALANCE1
CURR1 = currency (indexed)

Table 2:
fieldname: CURR1, AMOUNT1, TRX_TYPE
trx_type may contain 'SELL' or 'BUY '

If trx_type = 'SELL' then BALANCE1 in Table 1 will be DEDUCTED BY AMOUNT1.
If trx_type = 'BUY ' then BALANCE1 in Table 2 will be ADDED BY AMOUNT1.

Sometimes the formula is not processed properly, so for example:
trx_type = 'SELL' and AMOUNT1 = 25
then the BALANCE1 in table 1 should be DEDUCTED BY 25 but sometimes it's not.
It is sometimes deducted by 75 (25 x 3 times).

Could you please tell me what's wrong with my program?

Thank you so much for your kind help,
Regards,