Reporting: Availability indicator

@ncastaneda the proposed indicator is composed of:

• health - conducted at inventory level.
• viability - conducted at inventory level.
• quantity sufficiency - conducted at inventory level.

Let's focus on viability. There are potentially multiple viability tests (and their results) per inventory.

I assume you want only the results of the last test. Even so:

1. What is sufficient viability threshold so that the material considered viable?
2. If the test is 10 years old, how do you consider the time since the test in marking something as sufficiently viable?