TinyDB is typically used for data persistence across Screen switching and across runs of the project.
The NameSpace is the XML file name used for storage of tags and values in each TinyDB instance.
Since you only have one Screen, and you are not accumulating data for subsequent analysis, you might as well use global variables.
(I notice you don't have a single global variable. Did you miss that chapter?)
http://www.appinventor.org/bookChapters/chapter16.pdf
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