Basing TA on the Open value is fraught with risk. For example, different data providers quote the FTSE100 Open as the previous day's Close, the value at 08:00am or the value at 08:02am. Overnight gaps mean such discrepancies can be significant. The FTSE is an index that actually has a closed session overnight, i.e. it is not being continuously re-calculated. But spreadbet markets derived from the FTSE (as well as Forex etc.) are open throughout the 24 hours, so Open in that context has much less meaning.