Selling goods and services both together means that you need to consider their treatment separately.

First and foremost you must understand that provided this service is just setting up the goods (i.e. a machine), it’s recognized alongside with the revenue from the sale of the item itself. Now provided though that this service is something else than just setting the item up, it needs to be recognized separately from the revenue of the item itself. 

Sale of the good is apparently easy – the revenue is recognized at the time the risks and rewards of the ownership are transferred to the new owner. However, services related to the item, which are also provided over a longer period (i.e. longer than a month or so), are recognized into revenue on the income statement over the same period the service is to be provided. For an example, if the service is to be provided over 2 years, the revenue from it is spread over the same 2 years.

Shoving all the revenue onto one period doesn’t really reflect truly and fairly on your income for the period – the current and future ones. In addition, you’re making expenses related to the sale in future periods, so why should you show the revenue in just one period. It’s far more accurate approach to really show the revenue spread over the period the service is really provided.