Plan for the Easy Gaps Hypotheses

· [ plotting, out-damned-spot ] · @pentronik

In the gaps hypotheses post, I listed out a bunch of ideas I have for what is causing the dot-or-gap blemishes when drawing closed loops. Some of the proposals are actually quite easy to test. So, for purposes of the scientific method, I will now write out my plan for testing several of those, and hazard an interpretation of what different results might mean.


The test plot shall be a 8x11” page in vertical orientation (long edge is in the Y-direction). On the page shall be drawn an array of concentric circles up to 1-inch in diameter. These concentric circles shall be arranged in rows and columns. Each page that is rendered shall be annotated either automatically or by hand with a note indicating what is to be tested. The circles will be drawn such that the pen starts and finishes always at the same angle for all circles. This angle will be indicated with a line inside the smallest circle.

// TODO(pentronik): Add an illustration.


This plan is for tackling the easiest hypotheses first. These are mostly the materials related questions.


If the issue reproduces, then the problem is still present. Sync the repo back to current and see if the plot still works and can still reproduce the issue. In either case, proceed.

If the issue is present, then the test figure is fit for this purpose. If not, do not proceed and work on the test figure until it does reproduce the issue.


  1. The problem is the pen is old and weak.

Proposal: Test with a fresh pen. Test with a different pen. I have some Isograph technical pens now, so test with those.

If the problem reproduces with a fresh pen that has good flow, it is not the pen that is at issue here.

  1. The problem is that I am not using the same pen every time and this is confusing.

Proposal: draw the same sheet several times with the same pen without changing anything. Do the gaps reproduce identically?

If the problem persists through all the sheets, then we know that the plotter is behaving in a very reproducible way, and that the pen has not shifted.

  1. The problem is that I am not putting the pen in the holder consistently.

Proposal: If the previous plot reproduced the issue, try plotting a sheet, and then rotating the pen 45º and plotting again.

If the issue goes away for some angle, then it is a pen issue. It may also be pen specific; I’ll have to find the angle for each pen that avoids this issue.


In this post I have laid out the beginnings of checking off some of these hypothesized reasons for the dots or gaps in the plots, and listed experiments for testing them. Stay tuned for test results.

@pentronik    :fountain_pen: