Method of calculation Alternate Qnt Instead Of Main Qnt

hi,
i just want to change the "based on Quantity" under Type of Calculation with class of payment voucher to alternate qnt

Code:

[#Field: CI Value]
QtyCalc : $$Total:VCHBilledQty * $$AsRate:$ClassRate

i meant multiple the value basis to alternate qnt instead of normal quantity


hope some one will help

 

[system : formula]
first alt qty : $$CollectionField$$String:$BilledQty:"Secondary"):1:InventoryEntries

in ledger entries field level call
$$Number@firstaltqty * $$Number:the rate % field

 

this is the default code

Code:

[#Field: CI Value]
QtyCalc : $$Total:VCHBilledQty * $$AsRate:$ClassRate

then now should i use like below

Code:

[#Field: CI Value]
QtyCalc : $$Number:@firstaltqty * $$Number:the rate % field

[system : formula]
first alt qty : $$CollectionField:($$String:$BilledQty:"Secondary"):1:InventoryEntrie

 

i tried but not working