The http://drupal.org/project/physical module provides a new "physical_weight" field. The attached patch adds support for this field as a destination.
This would best go into the Physical Fields module itself. This patch would need the following changes:
1. Add physical_weight_migrate_api().
2. Rename physical_weight_field.inc to physical_weight.migrate.inc, so hook_migrate_api() can be found automatically.
3. Add physical_weight.migrate.inc to physical_weight.info.
I see there's a separate request with some proposed code (no formal patches) at #1626578: Add Migrate support to 'Physical Fields', one of these should be marked as a duplicate of the other.
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