Ask HN: Forecasting of Hardware/Wearables Startup

This is my first time getting into the wearables/hardware market and I'm looking for guidance on how forecasting hardware/wearables development is different from the software/apps space.

My google searches have not been fruitful in this regard. I have COG for each component at retail pricing, but how does that change in manufacturing? How do you forecast manufacturing cost, packaging, returns, etc?

Is anybody able to share a breakdown of how this is done, or advice to someone new to this space?