Total Function in Vizlib Table does not work well

[ivanyang25]

Dear Experts

Currently I am using extention Vizlib Table to aggregate some biz data

DC Stock: INV_CAL

BTP Unship:Rep_Unship_CAL

BTP In-Transit: Transit_CAL

Real Order: BLK_CAL

I am working on a new column [Need Repl Orders]

[Need Repl Orders]= Real Order - BTP InTransit - BTP Unship - DC Stock

I wanna set it to zero when the result is minus. Therefore I set the expression as below

However, when I open total function in this table, the result is always zero

As you can found in the below screeshot, the result should be 202 but not zero

I try quite a lot ways still can't correct it. Could you kindly help advise how to make it happen?

You could also check my code in loading page as below as well

Thanks for your advise in advance

Ivan