The structure of the Being of what is ready-to-hand as equipment is determined by references or assignments. In a peculiar and obvious manner, the 'Things' which are closest to us are 'in themselves' ["Ansich"]; and they are encountered as 'in themselves' in the concern which makes use of them without noticing them explicitly-the concern which can come up against something unusable. When equipment cannot be used, this implies that the constitutive assignment of the "in-order-to" to a "towards-this" has been disturbed. The assignments themselves are not observed; they are rather 'there' when we concernfully submit ourselves to them [Sichstellen unter sie]. But when an assignment has been disturbed-when something is unusable for some purpose-then the assignment becomes explicit. Even now, of course, it has not become explicit as an ontological structure; but it has become explicit ontically for the circumspection which comes up against the damaging of the tool. When an assignment to some particular "towards-this" has been thus circumspectively aroused, we catch sight of the "towards-this" itself,  and along with it everything connected with the work-the whole 'workshop'- as that wherein concern always dwells. The context of equipment is lit up, not as something never seen before, but as a totality constantly sighted beforehand in circumspection. With this totality, however, the world announces itself.
Similarly, when something ready-to-hand is found missing, though its everyday presence [Zugegensein] has been so obvious that we have never taken any notice of it, this makes a break in those referential contexts which circumspection discovers. Our circumspection comes up against emptiness, and now sees for the first time what the missing article was ready-to-hand with, and what it was ready-to-hand for. The environment announces itself afresh. What is thus lit up is not itself just one thing ready-to-hand among others; still less is it something present-at-hand upon which equipment ready-to-hand is somehow founded: it is in the 'there' before anyone has observed or ascertained it. It is itself inaccessible to circumspection, so far as circumspection is always directed towards entities; but in each case it has already been disclosed for circumspection. 'Disclose' and 'disclosedness' will be used as technical terms in the passages that follow, and shall signify 'to lay open' and 'the character of having been laid open.' Thus 'to disclose' never means anything like 'to obtain indirectly by inference'.1
1 In ordinary German usage, the verb 'erschliessen' may mean not only to 'disclose' but also-in certain constructions--to 'infer' or 'conclude' in the sense in which one 'infers' a conclusion from premises. Heidegger is deliberately ruling out this latter intrpretion, though on a very few occasions he may use the word in this sense. He explains his own meaning by the cognate verb 'aufschliessen', to 'lay open'. To say that something has been 'disclosed' or 'laid open' in Heidegger's sense, does not mean that one has any detailed awareness of the contents which are thus 'disclosed', but rather that they have been 'laid open' to us as implicit in what is given, so that they may be made explicit to our awareness by further analysis or discrimination of the given, rather than by any inference from it.