Project workspace
Keep a separate part list for each build. Store each part's real-world size once, and the model size is worked out at the project's scale. Change the scale and every part updates.
Projects are saved in this browser only, using localStorage. Nothing is uploaded. Clearing site data or using private browsing deletes them, so use Export JSON to keep a backup or move projects to another device.
Backup and transfer
Imports are checked before anything is saved. The file must be a Miniature Scale Lab export under 1 MB. Unknown fields are dropped, as are invalid numbers, negative sizes and impossible scales, and text is length-limited. Imported projects are added to yours, never overwriting them.