Portal Calculation help

[atlanticind]

Im currently using a portal to relay certain information from my main database, the information that is related between the two are the fields of 'Brand' and 'Part Number'.

 

The only other fields i have in my portal will be

 

1. Sale Or Purchase (a drop down list to select either sale or purchase).

2. Quantity

3. Date

4. Price

Is there any kind of calculation so that when i select either the 'sale' or 'purchase' option in the drop down list that it will either add or subtract the quantity i then enter into my quantity field, this way my stock list can keep up to date with the correct quantities?

 

Example

Brand - ddd

Part No. - 123

Sale selected

Quantity - 3

Date - 22/02/2013

 

so after i have entered all of this data because i have sold 3 i need my calculation to take 3 away from the overall stock, and for the calculation to add 3 if this was a purchase

 

hope this makes sense

 

thank you

Edited May 31, 2016 by Lee Smith
Removed General Topic Notice

[Lee Smith]

See if this helps.

https://www.geistinteractive.com/2014/03/11/simple-filemaker-transactions-video/

Lee