Certified logger altitude recording?

How do current certified loggers determine altitude? Being some are plumbed to external pitot/static and some are cockpit pressure only, what differences are expected?

Does your mechanical altimeter (especially 57mm size) read close to your "glide caculator" altitude?

Are loggers solely dependent on pressure altitudes or is GPS altitude comparison ever included in the algorithms?

Seems one would be more likely to "bust" min/max altitudes using cockpit pressure loggers.