Text changes size when zooming in and out due to design.
Cause:
Floating text always changes size when zooming in and out. This behavior is by design of Excel Data Map.
Solution:
Create text that does not change size when zooming in and out, or create floating text in a higher magnification.
Do one of the following:
1) Create text that does not change size:
a) Select the 'View' menu.
b) Select 'Title' or 'Subtitle'.
c) Type the text in the displayed box.
d) (Optional) Format the text or resize the box.
2) Create text that is correctly positioned and sized when the map is enlarged:
a) Zoom in to the desired magnification.
b) Click 'Add Text' toolbar button.
c) Type the text while in the higher magnification.
d) (Optional) Format the text.