A measure of implied volatility on Wall Street on Black Friday touched the highest level since around September as futures for the Dow Jones Industrial Average [: DJIA] and the S&P 500 index /zigman2/quotes/210599714/realtime SPX -1.17% , looked set to tumble amid concerns of a fast-spreading strain of coronavirus, which was identified in South Africa, Hong Kong and Israel and was already leading to travel restrictions. The CBOE Volatility Index /zigman2/quotes/210598281/delayed VIX +15.42% jumped by about 40% Friday morning, trading around 25.4, which would mark the highest level for the index since around Sept. 20 and mark the biggest daily jump for the measure since late January, according to FactSet data. The index, also known as the VIX, for its ticker symbol, has become well known as Wall Street's "fear gauge," since it was created in the early 1990s. The VIX itself, which uses S&P 500 options to measure trader expectations for volatility over the coming 30-day period, tends to rise as stocks fall and is often therefore referred to as a guide to the level of investor fear. It had been trading below its historic average of around 19.5.