QuickBooks items can be set up with multiple units of measure and be used on various transactions such as estimates, sales orders and invoices. If unit of measure is specified, QuickBooks will use values for Qty and Rate as entered by the user but does a conversion before making this available to 3rd party add-ons like Method.

Resolution

QuickBooks allows the use of items with multiple units of measure allowing various inputs for Qty and Rate depending on how the item is bought and/or sold on transactions like estimates, sales orders and invoices. However, when you work with 3rd party applications that talk to QuickBooks like Method, you'll notice the fields for Qty and Rate are converted before they are made available via the SDK. This is not a error of Method or any 3rd party application but rather a limitation of the QuickBooks SDK. Method is not doing any extra calculations. That's just how QuickBooks makes the data available. 

The SDK uses the Qty of the base unit (usually the smallest unit used to track a certain type of item) as the new Qty made available to Method. In order to ensure the transaction line amount (Amount = Qty * Rate) has not changed, the Rate must be recalculated before being made available. These new Qty and Rate values are then sent to Method.

It may be possible to implement 'work arounds' to meet specific request but designers should proceed with a high degree of caution and understand it is generally discouraged by Method Integration.