SINGAPORE: Financial markets around the world will open on Wednesday with a tinge of apprehension, not just because of developments in Greece or China, but because of an extra second.

A “leap second” is being added to the world’s clocks at midnight GMT on Tuesday, which could test the extremely sensitive trading systems of the modern algorithmic era, beginning with markets in Asia.

The decision to add a leap second has been taken by the International Telecom-munication Union, a UN body, to harmonize atomic time with the sometimes imprecise time taken by the earth to rotate around its axis.

While there have been several occasions since 1972 that leap seconds have been added to world clocks, this is the first time since 1997 that such a tweak is happening on a working day and in a high-speed electronic trading environment.

The majority of global equity trading and a significant proportion of trading in bonds, currencies, commodities and derivatives, is done on electronic platforms governed by the international Financial Information Exchange (FIX) protocol.

“On the FIX systems, the tolerance limits on an order may make it look stale if the clocks are out of sync, which is the biggest issue,” said one head of electronic sales at a European brokerage in Hong Kong.

Stock exchanges, brokers and investment banks said they were working with their vendors and clients to ensure their internal clocks were brought into line.

“No one’s actually expecting a big impact. Tolerance limits are usually more than a second anyway because clocks are not always exactly aligned between clients and broker,” the head of electronic sales said.

Intercontinental Exchange, a major network of exchanges for financial and commodity markets, said it would delay market openings which would normally occur between 2300 GMT on Tuesday and 0001 GMT Wednesday by varying amounts of time.