---
title: Chance and forecasts: how the terrarium simulator works
description: Two things are random; everything else repeats exactly. Random: each day's death roll, and grey mould's first infection. Repeatable: water, temperature,...
url: https://glassjar.garden/guide/how-it-works/chance-and-forecasts/
---

How it works

# Chance and forecasts

Two things are random; everything else repeats exactly.

- Random: each day's death roll, and grey mould's first infection.
- Repeatable: water, temperature, growth and health.
- Before sealing, the forecast runs the jar several ways and counts what should be alive in a year.

## Stats

- Year survival: e^-(sum of the year's hazards)

[See it in a jar](https://glassjar.garden/?guide=how-it-works/chance-and-forecasts)

[← Care](https://glassjar.garden/guide/how-it-works/care/) · [Checked against real jars →](https://glassjar.garden/guide/how-it-works/checked-against-real-jars/)