calculate the open and close on a minute chart with historical ticks

I wanted to calculate the open and close on a minute chart with historical ticks.
Does the minute chart
1/ open at 00.00 and closes at 59.999 or
2/ open at 00.00 and closes at 60.00?

If 1/ then .001 is missing and can amount to a lot for long term backtesting since the minute chart is not exactly 1 minute?

Is there an industry-wide convention on the answer or each participant has its own rule?

thanks

maxoup
 
Back
Top