School chalks / 
British Standards Institution 
 - 6 leaves :  illustrations ;  20 cm. 
 - British standard ;  BS 3060 : 1958 .
 - British standard ;  BS 3060 : 1958 .
<br/><br/><label>Subjects--Topical Terms: </label><br/>Chalk--Standards--Great Britain<br/>Chalk--Standards