diff --git a/figures/clocks/reference-clock.pdf b/figures/clocks/reference-clock.pdf
new file mode 100644
index 0000000..1016fd7
Binary files /dev/null and b/figures/clocks/reference-clock.pdf differ
diff --git a/figures/clocks/src/reference-clock.py b/figures/clocks/src/reference-clock.py
new file mode 100755
index 0000000..42b1d66
--- /dev/null
+++ b/figures/clocks/src/reference-clock.py
@@ -0,0 +1,176 @@
+#!/usr/bin/env python3
+
+__doc__ = \
+"""
+Generate a figure showing the alignment of an external clock
+referenced to a WR clock as could be seen on an oscilloscope.
+"""
+
+import matplotlib.pyplot as plt
+import numpy as np
+import scipy.signal as sig
+
+### Functions
+
+def plot_signal( ax, t, t_edge, s_edge, name=None, box_kw={'hatch': '/'}, line_kw={}, annotate_t_edge=True,**plot_kw):
+    """
+    Plot a signal directly on an axis.
+    Uses t_edge to trigger height
+    """
+    lower = (t > t_edge)
+    upper = (t > t_edge + s_edge)
+
+    # merge dictionaries correctly
+    line_kw = { **plot_kw, **line_kw }
+
+    # plot lower and upper lines
+    l = ax.plot(t, lower, **line_kw)
+    
+    ## update colour when plot_kw was empty
+    plot_kw = { **plot_kw, **{'color': l[0].get_color()} }
+    line_kw = { **plot_kw, **line_kw }
+    box_kw = { **plot_kw, **box_kw }
+
+
+    l2 = ax.plot(t, upper, **line_kw)
+
+    # plot the shaded box of width t_sigma
+
+    l3 = ax.fill_between(t, upper, lower, **box_kw)
+
+    # annotations
+    if name is not None:
+        if annotate_t_edge:
+            # annotate t_edge
+            y = 1
+            ax.annotate("$t_\mathrm{{{}}}$".format(name),
+                    xy=(t_edge, y), xytext=(t_edge-3, y),
+                    va='top', ha='center'
+            )
+
+        # annotate s_edge
+        y = 0.3
+        annotate_width(ax, "$\sigma_\mathrm{{{}}}$".format(name), t_edge, t_edge+s_edge, y)
+
+    return [l, l2, l3]
+
+def plot_diff_time(ax, name, t_1, t_2, y, vline_kw={}, va='bottom'):
+    ax.axvline(t_1, **vline_kw)
+    ax.axvline(t_2, **vline_kw)
+
+    arrow_kw = {
+            'va':va,
+    }
+
+    annotate_width(ax, name, t_1, t_2, y)
+
+def annotate_width(ax, name, x1, x2, y, text_kw={}, arrow_kw={}):
+    default_arrow_kw = dict(
+            xy = (x1, y),
+            xytext = (x2,y),
+            arrowprops = dict(
+                arrowstyle="<->",
+                shrinkA=False,
+                shrinkB=False
+            ),
+    )
+
+    default_text_kw = dict(
+            va='bottom',
+            ha='center',
+            xy=((x1+x2)/2, y)
+    )
+
+    an1 = ax.annotate("", **{**default_arrow_kw, **arrow_kw})
+    an2 = ax.annotate(name, **{**default_text_kw, **text_kw})
+
+    return [an1, an2]
+
+
+## Main
+def main():
+    """
+    Create a figure with two signals at times t1 and t2 (accuracy s1, s2)
+    as compared to a reference timer tr (sr), with annotations.
+    """
+    
+    t = np.linspace(0, 100, 1e3)
+
+    t_A = 40
+    t_B = 70
+    t_ref = 10
+
+    s_A = 10
+    s_B = 10
+    s_ref = 5
+   
+    box_kw = {
+            "alpha": 0.3,
+            "hatch": '\\',
+    }
+    line_kw = {
+            }
+
+    vline_kw = {
+            "linestyle": '--',
+            "color": "k",
+            }
+ 
+    fig, axs = plt.subplots(3,1,sharex=True, gridspec_kw={'hspace': 0});
+
+    # Overall styling
+    axs[-1].set_xticks([])
+    axs[-1].set_xticklabels([])
+    for ax in axs:
+        ax.set_ylim(-0.2, 1.2)
+        ax.set_yticks([])
+        ax.set_yticklabels([])
+        ax.grid()
+
+    # Create the plots
+    i = -1
+
+    # Signal A
+    i+=1
+    y = 0.6
+    axs[i].set_ylabel("Signal A")
+    plot_diff_time(axs[i], "$t_\\mathrm{A}}$", t_ref, t_A, y, vline_kw=vline_kw)
+    plot_signal(axs[i], t, t_A, s_A, name="A", box_kw=box_kw, line_kw=line_kw, annotate_t_edge=False)
+
+    # Reference
+    i+=1
+    axs[i].set_ylabel("Reference")
+    axs[i].axvline(t_ref, **vline_kw)
+    plot_signal(axs[i], t, t_ref, s_ref, name="ref", box_kw=box_kw, line_kw=line_kw, color='g')
+    plot_diff_time(axs[i], "$t_\\mathrm{C}$", t_A, t_B, 0.3, vline_kw=vline_kw)
+
+    # Signal B
+    i+=1
+    axs[i].set_ylabel("Signal B")
+    plot_diff_time(axs[i], "$t_\\mathrm{B}}$", t_ref, t_B, y, vline_kw=vline_kw)
+    plot_signal(axs[i], t, t_B, s_B, name="B", box_kw=box_kw, line_kw=line_kw, color='purple', annotate_t_edge=False)
+
+
+    return fig, 0
+
+
+if __name__ == "__main__":
+    from argparse import ArgumentParser
+    import os.path as path
+
+    parser = ArgumentParser(description=__doc__)
+    parser.add_argument("fname", metavar="path/to/figure[/]", nargs="?", help="Location for generated figure, will append __file__ if a directory. If not supplied, figure is shown.")
+
+    args = parser.parse_args()
+
+    if args.fname is not None and path.isdir(args.fname):
+        args.fname = path.join(args.fname, path.splitext(path.basename(__file__))[0] + ".pdf")
+
+    ###
+    fig, _ = main()
+
+    if args.fname is not None:
+        plt.savefig(args.fname)
+    else:
+        plt.show()
+