Put existing product in stock with serial number

Hi all, I’m testing ERPNEXT for our company. We are manufacturing low quantities of precision measurement equipment. My first test with ERPNEXT is to put in our current stock of finished instruments, but for some reason I cannot make an “item” that allows the “has serial number” to be checked. Tracking instruments by their serial is required as the need recalibration after some time. What is the best option to add already manufactured instruments to the stock with their serial included?

Secondary question is how I set up the “has variants” as our instrument indeed comes in 2x2 variants?

Welcome PR650

These docs and q&a notes may help answer your questions -

https://erpnext.org/docs/user/manual/en/stock/item

Serial numbers automatically entered in delivery note
Serial number in Delivery note

Item Variants common question