Markers draw reference price levels from previous periods onto the current chart, so you can see where today is trading relative to last week's high or last month's close without drawing anything by hand.
They open from the marker icon on the left toolbar. The dialog has seven panels: Last price, then a developing and a previous panel for each of day, week and month.
Last Price
Last price draws a line at the current traded price, with a colour swatch beside it.
Extend lines carries the line across the full chart width instead of stopping at the current candle.
Dashed line draws it broken rather than solid, which is worth using when several markers are on screen at once and you want to tell them apart at a glance.
Show instrument label prints the instrument name against the line. This matters on aggregated or multi-chart layouts, where several price lines can sit close together and the label is the only thing telling you which is which.
Developing and Previous Periods
The remaining six panels — Developing Day, Previous Day, Developing Week, Previous Week, Developing Month, Previous Month — all work the same way, and each has the same set of controls.
A developing period is the one currently in progress. Its levels move as the period builds: the developing day's high updates every time price makes a new high today.
A previous period is closed. Its levels are fixed, and they are the ones traders watch as support and resistance — yesterday's high and low, last week's close, the prior month's range.
Each panel lets you enable the period and choose which of its levels to draw, along with the colour, line style and labelling for each. Turning on every level across all six panels will bury the chart, so most setups run one or two: previous day levels for intraday work, previous week and month for swing context.