Hello Craig,
for information,
actually I understand now why I had a difficulty here.
In a meta data source, when I create a new numerical point "example", "example" is not available in the script context.
Even if I save it, open an other point for edition and come back to "example" to edit it, it is still not available in the script context. Saving the data source doesn't help.
I am forced to close the meta datasource, to reopen it for edition and then only when I edit the newly created point "example" (or any other point), "example" is available in the script context.
Alex