This Rule is rarely applied as it only comes into play when you can't successfully classify your goods using Rules 1 to 3. Goods which cannot be classified in accordance with Rules 1 to 3 are classified under the heading appropriate to the goods to which they are most akin.
Rule 4 enables you to classify goods that are similar to others, but can't be directly related. In most cases you should be able to locate an accurate description of your goods due to the comprehensive nature of the classification that the Tariff uses.
In classifying using Rule 4, you have to compare the presented goods with similar goods in order to determine which other items the presented goods are most similar, or most akin to. Kinship can depend on many factors such as description, character and purpose. In the past - before they were given their own commodity code - computers, because of their kinship with adding machines were given the commodity code for adding machines.