<P> The name of local time typically changes when DST is observed . American English replaces standard with daylight: for example, Pacific Standard Time (PST) becomes Pacific Daylight Time (PDT). In the United Kingdom, the standard term for UK time when advanced by one hour is British Summer Time (BST), and British English typically inserts summer into other time zone names, e.g. Central European Time (CET) becomes Central European Summer Time (CEST). </P> <P> The North American English mnemonic "spring forward, fall back" (also "spring ahead ...", "spring up ...", and "...fall behind") helps people remember which direction to shift clocks . </P> <P> Changes to DST rules cause problems in existing computer installations . For example, the 2007 change to DST rules in North America required that many computer systems be upgraded, with the greatest impact on e-mail and calendar programs . The upgrades required a significant effort by corporate information technologists . </P> <P> Some applications standardize on UTC to avoid problems with clock shifts and time zone differences . Likewise, most modern operating systems internally handle and store all times as UTC and only convert to local time for display . </P>

Who changes the time for daylight saving time