A meter that increases the statistical probability of triggering a bonus feature based on symbol elimination or winning sequences.

### Incremental Advantage
Each winning combination or symbol elimination adds a unit to the meter, which directly correlates to an increase in the internal bonus trigger probability.
### Visual Tension
The meter often has visual milestones that signal the player is entering a 'high-probability' zone, where the bonus could trigger at any moment.
### Dynamic Triggering
Because it's probability-based, the bonus can trigger early in the progression or wait until the meter is nearly full, keeping the experience unpredictable yet rewarding.

### Fairness and Persistence
It rewards long play sessions by ensuring that every small win contributes to a higher chance of a big bonus, preventing the feeling of a 'wasted' spin.
### Psychological Engagement
Watching a probability meter rise creates a powerful 'near-miss' psychological effect, encouraging players to stay for 'just one more spin' to see if the increased odds pay off.
### Strategic Pacing
The escalating tension keeps the base game exciting even during periods of smaller payouts, as the underlying probability of a major feature is constantly improving.