your code starts by closing any selection "pdb.gimp_selection_none(image)"

I'm just an old scheme writer but I'm sure something is wrong with maths

protractor from 'Simple path shapes' starts as below
# Draw_Protractor Rel 1 [download: https://gimplearn.net/viewtopic.php?t=3&t=175#p512]
# Created by Tin Tran https://gimplearn.net
# Comments directed to http://gimpchat.com or http://gimpscripts.com

pdb.gimp_selection_none(image)
if sel == False:
x1 = 0
y1 = 0
x2 = W
y2 = H

W = float(abs(x2-x1))
H = float(abs(y2-y1))
radius = min(W,H)/2.0
midx = x1 + (W/2.0)
midy = y1 + (H/2.0)

Nah Nah Nah (close but no cigar) In protractor you left me with a selection i did not start with, in ruler you also left a selection i did not start with and the horizontal rulers did not cover the entire width of the image

I'm using 'Simple path shapes centered' Rel 9 on a 600x400 image with no selection in place and the output is below

The preferred output for using 'Simple path shapes centered' Rel 9 on a 600x400 image with no selection in place and the output is as per the 'draw percentage ruler' script below

'Simple path shapes' now returns a selection with the path due to this line added at the end↓

An existing selection should be saved to a channel and a marker set to TRUE at the start of the script so it can be returned at the end

MareroQ yes that looks perfect but I gather you increased the image size

'Draw percentage ruler' functions perfectly, if you can get 'Simple path shapes' to work the same for all shape choices that would be great

Good morning MareroQ, your ruler still does not produce the desired outcome without a selection in place [such as full image size] should have output as below↓ (done after select-all)

but instead the rulers are incorrect

Also the length of the divisions on the ruler are tied to the stroke width rendering it impracticable to use the stroke feature.
at the start of the script if no selection is found select all and set your [in selection] toggle to yes remembering to set your return selection marker to no and run your script as if a selection was made
perhaps make the length of the divisions in ruler relate to the resize layer lengths