From aed72ab0e93e8a80603c8a1b0dd3b9267d7bf042 Mon Sep 17 00:00:00 2001
From: j-w9 <295470691+j-w9@users.noreply.github.com>
Date: Sat, 17 Oct 2026 11:59:44 -0400
Subject: [PATCH] PIDReview: explain how the step response is found and when it
 is empty

---
 PIDReview/PIDReview.js | 9 +++++++++
 PIDReview/index.html   | 5 ++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/PIDReview/PIDReview.js b/PIDReview/PIDReview.js
index d8c50ada..7cd7efb1 100644
--- a/PIDReview/PIDReview.js
+++ b/PIDReview/PIDReview.js
@@ -132,6 +132,7 @@ function reset() {
         step_plot.data[i].x = []
         step_plot.data[i].y = []
     }
+    document.getElementById("step_note").hidden = true
     for (let i = 0; i < Spectrogram.data.length; i++) {
         Spectrogram.data[i].x = []
         Spectrogram.data[i].y = []
@@ -1048,6 +1049,7 @@ function redraw_step() {
         step_plot.data[plot_index].x = []
         step_plot.data[plot_index].y = []
     }
+    document.getElementById("step_note").hidden = true
     if (valid_sets == 0) {
         Plotly.redraw("step_plot")
         return
@@ -1105,6 +1107,9 @@ function redraw_step() {
     // Pre-calculate inverse
     sn = array_inverse(sn)
 
+    // Count of sets with at least one step estimate
+    let sets_with_steps = 0
+
     // For each data set
     for (let j = 0; j < num_sets; j++) {
         if (PID.sets[j] == null) {
@@ -1189,6 +1194,7 @@ function redraw_step() {
                 // No good steps, skip this set
                 continue
             }
+            sets_with_steps += 1
 
             // Plot mean
             step_plot.data[plot_index+1].x = time
@@ -1201,6 +1207,9 @@ function redraw_step() {
 
     }
 
+    // Explain an empty plot
+    document.getElementById("step_note").hidden = (sets_with_steps > 0)
+
     step_plot.layout.yaxis.range = [0, 2]
     step_plot.layout.yaxis.autorange = false
 
diff --git a/PIDReview/index.html b/PIDReview/index.html
index c6b5cae8..6092bb77 100644
--- a/PIDReview/index.html
+++ b/PIDReview/index.html
@@ -248,8 +248,10 @@ <h2 style="text-align:center">
         Step Response
         <img id="TT_PID_StepResponse" src="../images/question-circle.svg" style="width: 1em; vertical-align: bottom"
             data-tippy-content="
-    Simulated PID response to a step input.
+    Closed loop step response estimated from the logged target and actual rates.
     Used to evaluate rise time, overshoot, damping, and stability.
+    Only parts of the flight where the target rate goes above 20 deg/s are used, so the analysis time needs some sharp stick inputs.
+    Grey lines are the estimate from each part, the coloured line is their mean.
     " />
     </h2>
 
@@ -257,6 +259,7 @@ <h2 style="text-align:center">
 </td></tr></table>
 
 <div id="step_plot" style="width:1200px;height:450px"></div>
+<p id="step_note" style="width:1200px; text-align:center" hidden>No step response: the target rate stayed below 20 deg/s in the analysis time. Select a section with some sharp stick inputs.</p>
 
 <table><tr><td style="width:1200px">
     <h2 style="text-align:center">