sentences:  Non-denominated postage was first introduced in the United Kingdom in 1989 for domestic mail, in part as a workaround to the problem of fast-changing rates.The British Post Office has issued "non-value indicated" Machins using textual inscriptions "1ST" and "2ND" to indicate class of service rather than a numeric value.It has since introduced a number of variations including those for worldwide and European use, for different weights, and for postcards.