Have you ever tried to count how many new words you tend to remember during, let’s say, ten days? Unless you are horribly meticulous, you probably don’t count the number of newly-acquired and yet awkwardly-used lexical units.
Frankly speaking, you don’t need this. First of all, it’s pointless. Even if you have learnt all the words they have in Muller’s dictionary, it doesn’t mean that they have become your active vocabulary. Second of all, you don’t need to do this with Muller’s dictionary…do it with your own! Create it using this resource, for example. It allows you to make your own dictionaries and study the words YOU like and YOU need. The tests provided will give you control over what you have remembered well and what requires more drilling.
Another advantage of the resource is that it provides the opportunity to see the words in lexical environment. Thus our memory tends to focus on prepositions used with the verbs or adjectives that can be used to describe a noun. Plus, some of the words (concrete nouns mostly) also have pictures that, as you know, do not allow our memory to forget the word owing to the association it retains.
The only great disadvantage of the resource IMHO is related to their sound pack. Well, no more spoilers. Just go there and check!