Calculating sales volume in food wholesaling systems

In a previous post, I described the issues with measuring quantities in warehousing systems. I showed how you could well need to measure more than just quantities purchased or sold. You often need to deal with the hierarchies of containers that goods are supplied in.

But while food wholesale systems will need to deal with quantities like I described in that post, they often have another layer of complexity. Items are often sold by:

Quantity
Weight
Quantity and Weight

Tracking Goods

We need to track different items differently.

Items that are sold by quantity work the same as any general warehousing system. Unit pricing is then applied to the quantity.
Items that are sold by weight are similar, but the weight will usually have decimal places. 3 decimal places is common. (And they want exact values, not approximations - so none of that float/real stuff). Unit pricing is applied to the weight.
Some items are sold by both quantity and weight, and both need to be tracked. For example, you might sell 20 fish, with a total weight of 24.217 kilograms. Again here, unit pricing is applied to the weight.

Where you track by both, the system needs to understand both how many fish or legs of lamb are left, and what weight of fish or legs of lamb are left. This is another area where accounting or BI systems that are designed by people who do not understand food wholesale fall short.