diff --git a/bare-metrics-gui/src/config.rs b/bare-metrics-gui/src/config.rs
index 974ebbe..b988b45 100644
--- a/bare-metrics-gui/src/config.rs
+++ b/bare-metrics-gui/src/config.rs
@@ -1,13 +1,31 @@
 use bare_metrics_core::structures::MetricKind;
 use serde::Deserialize;
+use std::collections::BTreeMap;
 
 #[derive(Deserialize, Default, Clone)]
 pub struct DashboardConfig {
     pub graphs: Vec<GraphConfig>,
 }
 
+#[derive(Deserialize, Clone)]
+pub enum MetricTransform {
+    Rate {
+        // Divisor in seconds. Would usually expect to see 1 (/sec), 60 (/min) or 3600 (/hour).
+        time_unit: f32,
+    },
+}
+
 #[derive(Deserialize, Clone)]
 pub struct GraphConfig {
     pub name: String,
     pub kind: MetricKind,
+    #[serde(default)]
+    pub transform: Option<MetricTransform>,
+}
+
+#[derive(Clone, Debug, Hash)]
+pub struct GraphRequest {
+    pub metric_name: String,
+    pub metric_labels: BTreeMap<String, String>,
+    pub derivation: Option<MetricTransform>,
 }
diff --git a/bare-metrics-gui/src/graph.rs b/bare-metrics-gui/src/graph.rs
index e4a9af7..ac84894 100644
--- a/bare-metrics-gui/src/graph.rs
+++ b/bare-metrics-gui/src/graph.rs
@@ -1,26 +1,27 @@
+use crate::config::MetricTransform;
 use anyhow::{anyhow, bail};
 use bare_metrics_core::structures::{
     Frame, MetricDescriptor, MetricId, MetricKind, UnixTimestampMilliseconds,
 };
 use bare_metrics_reader::{MetricsLogReader, SeekToken};
 use eframe::egui::{
-    Color32, Frame as EguiFrame, Galley, PointerButton, Pos2, Rect, Sense, Stroke, TextStyle, Ui,
-    Vec2,
+    Color32, Frame as EguiFrame, PointerButton, Pos2, Rect, Sense, Stroke, TextStyle, Ui, Vec2,
 };
 use hdrhistogram::Histogram;
 use log::{debug, error, info};
 use std::collections::{BTreeMap, HashMap};
 use std::io::{Read, Seek};
-use std::ops::{Mul, RangeInclusive};
+use std::ops::{DerefMut, Mul, RangeInclusive};
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::mpsc::{Receiver, Sender};
-use std::sync::{Arc, RwLock};
-use std::time::SystemTime;
+use std::sync::{Arc, Mutex, RwLock};
 
 /// Make a checkpoint every 10 minutes?
 /// This should probably be tunable since it will likely vary per-source ...
 pub const CHECKPOINT_EVERY_MILLISECONDS: u64 = 600_000_000;
 
+pub type StateCallbackHook = Arc<Mutex<Option<Box<dyn FnOnce() + Send + 'static>>>>;
+
 #[derive(Clone, Debug)]
 pub struct MetricsWindow {
     pub time_range: RangeInclusive<f64>,
@@ -157,6 +158,7 @@ pub enum MetricsLogReaderMessage {
 impl MetricsLogReadingRequester {
     pub fn new_manager<R: Read + Seek + Send + 'static>(
         reader: MetricsLogReader<R>,
+        on_initial_scan_done: StateCallbackHook,
     ) -> MetricsLogReadingRequester {
         let shared = Arc::new(MetricsLogReadingShared {
             current_window: RwLock::new(MetricsWindow {
@@ -177,9 +179,12 @@ impl MetricsLogReadingRequester {
         std::thread::Builder::new()
             .name("metricslogreader".to_string())
             .spawn(move || {
-                if let Err(err) =
-                    MetricsLogReaderManager::new_and_run(manager_shared_ref, reader, rx)
-                {
+                if let Err(err) = MetricsLogReaderManager::new_and_run(
+                    manager_shared_ref,
+                    reader,
+                    rx,
+                    on_initial_scan_done,
+                ) {
                     error!("Error in background log reader: {:?}", err);
                 }
             })
@@ -554,11 +559,19 @@ impl<R: Read + Seek> MetricsLogReaderManager<R> {
         Ok(metrics_window)
     }
 
-    fn run(&mut self) -> anyhow::Result<()> {
+    fn run(&mut self, on_initial_scan_done: StateCallbackHook) -> anyhow::Result<()> {
         info!("Starting manager");
         self.initial_scan()?;
         self.update_metric_descriptors();
         info!("Initial scan done.");
+        let mut the_func = None;
+        let mut callback_guard = on_initial_scan_done
+            .lock()
+            .map_err(|_| anyhow!("Can't lock"))?;
+        std::mem::swap(&mut the_func, callback_guard.deref_mut());
+        if let Some(on_initial_scan_done) = the_func {
+            on_initial_scan_done();
+        }
 
         while let Ok(msg) = self.rx.recv() {
             match msg {
@@ -637,6 +650,7 @@ impl<R: Read + Seek> MetricsLogReaderManager<R> {
         shared_ref: Arc<MetricsLogReadingShared>,
         reader: MetricsLogReader<R>,
         rx: Receiver<MetricsLogReaderMessage>,
+        on_initial_scan_done: StateCallbackHook,
     ) -> anyhow::Result<()> {
         let mut manager = MetricsLogReaderManager {
             shared_ref,
@@ -648,7 +662,7 @@ impl<R: Read + Seek> MetricsLogReaderManager<R> {
             checkpoints: Default::default(),
         };
 
-        manager.run()
+        manager.run(on_initial_scan_done)
     }
 }
 
diff --git a/bare-metrics-gui/src/main.rs b/bare-metrics-gui/src/main.rs
index 6a97e98..93da5d0 100644
--- a/bare-metrics-gui/src/main.rs
+++ b/bare-metrics-gui/src/main.rs
@@ -82,7 +82,9 @@ fn main() -> anyhow::Result<()> {
 
     let reader = MetricsLogReader::new(file).unwrap();
     let log_app_name = reader.header.application_name.clone();
-    let requester = MetricsLogReadingRequester::new_manager(reader);
+    // TODO we can attach a callback to this hook.
+    let init_hook_callback = Default::default();
+    let requester = MetricsLogReadingRequester::new_manager(reader, init_hook_callback);
 
     let dashboard_dir = appdirs::user_data_dir(Some("baremetrics"), Some("rei"), true)
         .unwrap()