Whenever something is not accomplished and resolved with a single action, progress towards an outcome is tracked using progress bars.
A progress bar is simply a lengthy box divided up into a number of sections. Whenever progress is made, one or more sections are crossed off or filled in. When all sections are crossed or filled, the outcome is reached.
For example, here is a progress bar with 5 steps, 2 of which are already completed:
| 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|
| X | X |
Progress bars are used to track stress, health, mana, long-term projects, villains' evil plans and many other things within the game.
When these rules speak of marking a progress bar, such as "mark two points of stress", it means to cross off or fill in the given number of boxes on the given progress bar.
Actions taken by choice that result in marking something can only be taken if there are still boxes available.
If all your "coins" boxes are filled, your character has spent all his money and you can no longer do things that require you to mark one or more coins.
When these rules speak of clearing points from a progress bar, you remove the cross or fill from it. This box is now available again.
Progress bars never go negative, so if you are asked to clear more boxes than you have crossed off, you simple remove all the crosses.
Progress bars can have status changes along their length, which activate as the bar gets progressively filled in.
Take for example, the standard harm progress bar, which has 2 boxes each in the lesser and moderate harm. Initially, the character will suffer -1 die for the next action, but once 3 boxes are filled in and he is moderately harmed, he takes -1 die to all actions, then at 4 boxes -2 dice and at 5 boxes (and a full harm bar) he is out and needs help.
Other progress bars have all kinds of status changes. A progress bar for the antagonist's evil project might have a status beyond which his machinations become obvious to the party. A character's long-term project bar might have a point at which it becomes useable or require maintenance.
Many progress bars can have variable lengths or divisions. For example, tougher characters can have more than the default harm boxes and so take more punishment before suffering negative effects.
This is especially noticeable in the bars for stress, mana burnout and coins. These can have boxes added by spending character points, giving characters more in each of these.
More complex bars such as the harm bar can get splits bought, where the player can split any box of his choosing in two by drawing in a vertical line in the center, turning one box into two. See Harm for more details.
As you have probably spotted, progress bars are very similar to progress clocks in Blades in the Dark. Using linear bars instead of round clocks simply makes it easier to add additional boxes.