So based on what I spotted in the source code of matplotlib’s _axes.py (https://github.com/matplotlib/matplotlib/blob/master/lib/matplotlib/axes/_axes.py#L1469-L1493):

    def plot(self, *args, scalex=True, scaley=True, data=None, **kwargs):
        """
        Plot y versus x as lines and/or markers.

        Call signatures::

            plot([x], y, [fmt], *, data=None, **kwargs)
            plot([x], y, [fmt], [x2], y2, [fmt2], ..., **kwargs)

        The coordinates of the points or line nodes are given by *x*, *y*.

        The optional parameter *fmt* is a convenient way for defining basic
        formatting like color, marker and linestyle. It's a shortcut string
        notation described in the *Notes* section below.

        >>> plot(x, y)        # plot x and y using default line style and color
        >>> plot(x, y, 'bo')  # plot x and y using blue circle markers
        >>> plot(y)           # plot y using x as index array 0..N-1
        >>> plot(y, 'r+')     # ditto, but with red plusses

I saw that I could use my axe to simply plot the positions of the indicators on in two dimensions. I got this:

Which is pretty much perfectly what I want right now. I did some fairly dirty mucking around with the data to get it to do this, essentially looking for where the row-to-row weight difference crosses a threshold from low-to-high.

# median filter with a rolling window: low pass filter
df['rolling4'] = df['weight'].rolling(4).median()

# normalise by looking for difference over 8 samples
df['diff'] = df['rolling4'].diff(periods=-8)

# Tag with True where the change is over 300g
threshold = 300.0
df['thresholded'] = (df['diff'] > threshold)

# Produce 'highlight' boolean where the threshold is True, AND
# the threshold for the previous row was False. This feels pretty clunky.
df['highlight'] = (df['thresholded'] == True) & (df['thresholded'].shift(1) == False)

# Now create a new dataframe with just the highlights in, and only the interesting columns
highlights = df[df['highlight']][['datetime', 'rolling4']]

That’s good isn’t it?