Trying to add a custom transaction line field (decimal number with default value). Transaction lines are actually item-related and there's a column for quantity and unit of the items per line. How to get the default value for this custom transaction line field to be the equivalent quantity in base units?

I don’t think a default value will accomplish what you are looking for. I think the default value is set during the record load process and at that point your line items won’t be entered so NS has nothing to calculate You would need to add a script or workflow that calculates the qty into the base qty during the item entry or record submit process (so after they click save) A workflow might be able to do this but would have to test if we can do a units join to get the conversion rate. A script should be fairly quick and easy to put together but I’m not 100% sure on that

Alan is right. Just wanted to add that there is the search field

Quantity in Transaction Units

that may be of use if you simply need this field for a search