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