<human>: Q: Why did the definition of film speeds change considerably?
 A: This revision also saw significant changes in the definition of film speeds in order to accommodate then-recent changes in the American ASA PH2.5-1960 standard, so that film speeds of black-and-white negative film effectively would become doubled, that is, a film previously marked as "18° DIN" would now be labeled as "21 DIN" without emulsion changes.
 Does the answer correctly answer the question

OPTIONS:
- yes
- no
<bot>: yes