# `Sidereon.GNSS.Data.Sp3ContentStartConvention`
[🔗](https://github.com/neilberkman/sidereon-ex/blob/main/lib/sidereon/gnss/data.ex#L106)

Cataloged relationship between an SP3 filename epoch and its first content
epoch.

Add `content_start_offset_s` to the filename epoch to obtain the declared
content start. The value is derived by the canonical core catalog.

# `t`

```elixir
@type t() :: %Sidereon.GNSS.Data.Sp3ContentStartConvention{
  content_start_offset_s: 0 | -86400,
  value: value()
}
```

# `value`

```elixir
@type value() :: :filename_epoch | :filename_epoch_minus_one_day
```

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*Consult [api-reference.md](api-reference.md) for complete listing*