Documentation

Lin/Log Scale Button

Enabling this toggle will add a Lin/Log Scale button to the toolbar. It will be displayed on the top right corner of the visual. 

With this button, users can dynamically choose which scale is used for the value axis (or axes) – linear or logarithmic.
lin_log_scale_button
This button will affect only the user's instance, and the default scale setting will be restored on a page refresh. If you want to change the default scale setting for all report users, use the Log Scale (Primary Y-Axis) or Log Scale (Secondary Y-Axis) properties.