Comments on the plugin.
1. Being able to use the Up/Dn or Left/Right arrow keys when the plugin is displayed prevents using these to move the chart. Only way round this is to disable the plugin.
Suggestion, disable arrow keys in plugin. + and - keys do the same thing anyway.
2. The way the plugin works is to go through each zoom sequentially. On very slow machines this is the same as +/- zooming and does not facilitate fast switching between set scales.
Suggestion, either; add a series of labels, ticks or buttons next to the slider that would enable a direct jump to an alternative scale, or replace the slider completely with a series of labels, buttons or ticks. If these could remember their last state ("current", "previous") by ticking, highlighting or coloring them, this would make it very easy to switch between them (detailed scale, planning scale). Current and previous would need to be updated if a different scale was chosen.
A toggle button at the bottom of the slider or a hot key would make switching back and forth between the last 2 scales selected even easier to achieve.
This is a very useful feature, for example, when doing checks of way points (detail scale) along a route
(planning scale), or having quick access to harbour entrance (detail scale) and overall (planning scale) when coming into port.