Forced Recalculation of Image Thumbnail in Container Field?

[macmasterservices]

I have two container fields, one named 'Image' and another named 'Image Thumbnail', the latter which uses this calculation resize the image:

GetThumbnail (Image; Total width cm * 5.1; Total height cm * 5.1)

This works fine, except that 'Image Thumbnail' is only created immediately after importing an image into the 'Image' field.

I would like to force regeneration of 'Image Thumbnail' whenever I change any parameters of the above calculation, such as the 5.1 factor. How can I automate this?

[John Mark Osborne]

Is the calculation storage option to "do not store calculation results -- recalculate when needed" checked? Making the calculation unstored should allow it to update automatically.

[macmasterservices]

1 hour ago, John Mark Osborne said:

Is the calculation storage option to "do not store calculation results -- recalculate when needed" checked? Making the calculation unstored should allow it to update automatically.

Originally my thumbnail field was a container field with a calculated result. I changed it to a calculation field, chose "Calculation result is 'Container'" in the lower left corner of the Specify Calculation window, and then selected "do not store calculation results -- recalculate when needed" in the Storage Options as you suggested, and voila! - Problem solved.

Thanks!