so does this mean that there is no point in getting tick by tick if the spx updates every 15 seconds?
I'm not fully aware of what you are trying to accomplish, but the spx is not a tradable vehicle, you go to spy, es etc to do that. for those tics are valuable imo.
z32000, ".....Continuously updated charts as trades occur. True tick by tick charting. Every tick received from the data feed is displayed and stored. Not a single tick is missed. Charts scroll automatically as new bars are added." http://www.sierrachart.com/index.php?file=Features.html I hope this helps. Tom