I write my presentations in Markdown, and use pandoc to compile into a PDF with latex's beamer.
An issue I frequently encounter is that I write too much, and so the content gets out of the slide.
Here is an example:
# Example
Example
I'm writing too much.
I really write too much.
$E=mc^2$
$F=ma$
$V=RI$
This is the equation for voltage.
Voltage is measures in Volts.
Resistance is measured in ohms ($\omega$).
Current is measured in amperes.
The previous one was an equation from physics.
It ties force with mass and acceleration. The equation before that was Einstein's.
Which results in:
As you can see, "was Einstein's" is out of the slide.
How can I have an horizontal ruler that tells me when there is no more space on the slide?
I'm using neovim.

