diff --git a/main/eis4.c b/main/eis4.c
index 22bd4fb..3c30ced 100644
--- a/main/eis4.c
+++ b/main/eis4.c
@@ -12,9 +12,11 @@
 #include "nvs_flash.h"
 #include "esp_netif.h"
 #include "esp_event.h"
+#include "esp_timer.h"
 
 #define AD5941_EXPECTED_ADIID   0x4144
 static EISConfig cfg;
+static uint16_t measurement_counter = 0;
 static EISPoint results[EIS_MAX_POINTS];
 static LSVPoint lsv_results[ECHEM_MAX_POINTS];
 static AmpPoint amp_results[ECHEM_MAX_POINTS];
@@ -25,8 +27,10 @@ static void do_sweep(void)
 {
     eis_init(&cfg);
 
+    uint32_t ts_ms = (uint32_t)(esp_timer_get_time() / 1000);
+    measurement_counter++;
     uint32_t n = eis_calc_num_points(&cfg);
-    send_sweep_start(n, cfg.freq_start_hz, cfg.freq_stop_hz);
+    send_sweep_start(n, cfg.freq_start_hz, cfg.freq_stop_hz, ts_ms, measurement_counter);
     int got = eis_sweep(results, n, send_eis_point);
     printf("Sweep complete: %d points\n", got);
     send_sweep_end();
@@ -132,8 +136,10 @@ void app_main(void)
                    lsv_cfg.v_start, lsv_cfg.v_stop, lsv_cfg.scan_rate, lsv_cfg.lp_rtia,
                    (unsigned long)max_pts);
 
+            uint32_t ts_ms = (uint32_t)(esp_timer_get_time() / 1000);
+            measurement_counter++;
             uint32_t n = echem_lsv_calc_steps(&lsv_cfg, max_pts);
-            send_lsv_start(n, lsv_cfg.v_start, lsv_cfg.v_stop);
+            send_lsv_start(n, lsv_cfg.v_start, lsv_cfg.v_stop, ts_ms, measurement_counter);
             int got = echem_lsv(&lsv_cfg, lsv_results, max_pts, send_lsv_point);
             printf("LSV complete: %d points\n", got);
             send_lsv_end();
@@ -149,7 +155,11 @@ void app_main(void)
             printf("Amp: %.0f mV, %.0f ms interval, %.0f s\n",
                    amp_cfg.v_hold, amp_cfg.interval_ms, amp_cfg.duration_s);
 
-            send_amp_start(amp_cfg.v_hold);
+            {
+                uint32_t ts_ms = (uint32_t)(esp_timer_get_time() / 1000);
+                measurement_counter++;
+                send_amp_start(amp_cfg.v_hold, ts_ms, measurement_counter);
+            }
             int got = echem_amp(&amp_cfg, amp_results, ECHEM_MAX_POINTS, send_amp_point);
             printf("Amp complete: %d points\n", got);
             send_amp_end();
@@ -171,7 +181,12 @@ void app_main(void)
             echem_ph_ocp(&ph_cfg, &ph_result);
             printf("pH: OCP=%.1f mV, pH=%.2f\n",
                    ph_result.v_ocp_mv, ph_result.ph);
-            send_ph_result(ph_result.v_ocp_mv, ph_result.ph, ph_result.temp_c);
+            {
+                uint32_t ts_ms = (uint32_t)(esp_timer_get_time() / 1000);
+                measurement_counter++;
+                send_ph_result(ph_result.v_ocp_mv, ph_result.ph, ph_result.temp_c,
+                               ts_ms, measurement_counter);
+            }
             break;
         }
 
@@ -197,8 +212,10 @@ void app_main(void)
         case CMD_OPEN_CAL: {
             printf("Open-circuit cal starting\n");
             eis_init(&cfg);
+            uint32_t ts_ms = (uint32_t)(esp_timer_get_time() / 1000);
+            measurement_counter++;
             uint32_t n = eis_calc_num_points(&cfg);
-            send_sweep_start(n, cfg.freq_start_hz, cfg.freq_stop_hz);
+            send_sweep_start(n, cfg.freq_start_hz, cfg.freq_stop_hz, ts_ms, measurement_counter);
             int got = eis_open_cal(results, n, send_eis_point);
             printf("Open-circuit cal: %d points\n", got);
             send_sweep_end();
@@ -252,7 +269,11 @@ void app_main(void)
 
             uint32_t n_per = (uint32_t)(cl_cfg.t_meas_ms / 50.0f + 0.5f);
             if (n_per < 2) n_per = 2;
-            send_cl_start(2 * n_per);
+            {
+                uint32_t ts_ms = (uint32_t)(esp_timer_get_time() / 1000);
+                measurement_counter++;
+                send_cl_start(2 * n_per, ts_ms, measurement_counter);
+            }
             ClResult cl_result;
             int got = echem_chlorine(&cl_cfg, cl_results, ECHEM_MAX_POINTS,
                                       &cl_result, send_cl_point);
diff --git a/main/protocol.c b/main/protocol.c
index 81d431c..17069f7 100644
--- a/main/protocol.c
+++ b/main/protocol.c
@@ -177,14 +177,17 @@ int send_keepalive(void)
 
 /* ---- outbound: EIS ---- */
 
-int send_sweep_start(uint32_t num_points, float freq_start, float freq_stop)
+int send_sweep_start(uint32_t num_points, float freq_start, float freq_stop,
+                     uint32_t ts_ms, uint16_t meas_id)
 {
-    uint8_t sx[20];
+    uint8_t sx[28];
     uint16_t p = 0;
     sx[p++] = 0xF0; sx[p++] = 0x7D; sx[p++] = RSP_SWEEP_START;
     encode_u16((uint16_t)num_points, &sx[p]); p += 3;
     encode_float(freq_start, &sx[p]); p += 5;
     encode_float(freq_stop, &sx[p]); p += 5;
+    encode_u32(ts_ms, &sx[p]); p += 5;
+    encode_u16(meas_id, &sx[p]); p += 3;
     sx[p++] = 0xF7;
     return send_sysex(sx, p);
 }
@@ -232,14 +235,17 @@ int send_config(const EISConfig *cfg)
 
 /* ---- outbound: LSV ---- */
 
-int send_lsv_start(uint32_t num_points, float v_start, float v_stop)
+int send_lsv_start(uint32_t num_points, float v_start, float v_stop,
+                   uint32_t ts_ms, uint16_t meas_id)
 {
-    uint8_t sx[20];
+    uint8_t sx[28];
     uint16_t p = 0;
     sx[p++] = 0xF0; sx[p++] = 0x7D; sx[p++] = RSP_LSV_START;
     encode_u16((uint16_t)num_points, &sx[p]); p += 3;
     encode_float(v_start, &sx[p]); p += 5;
     encode_float(v_stop, &sx[p]); p += 5;
+    encode_u32(ts_ms, &sx[p]); p += 5;
+    encode_u16(meas_id, &sx[p]); p += 3;
     sx[p++] = 0xF7;
     return send_sysex(sx, p);
 }
@@ -264,12 +270,14 @@ int send_lsv_end(void)
 
 /* ---- outbound: Amperometry ---- */
 
-int send_amp_start(float v_hold)
+int send_amp_start(float v_hold, uint32_t ts_ms, uint16_t meas_id)
 {
-    uint8_t sx[12];
+    uint8_t sx[20];
     uint16_t p = 0;
     sx[p++] = 0xF0; sx[p++] = 0x7D; sx[p++] = RSP_AMP_START;
     encode_float(v_hold, &sx[p]); p += 5;
+    encode_u32(ts_ms, &sx[p]); p += 5;
+    encode_u16(meas_id, &sx[p]); p += 3;
     sx[p++] = 0xF7;
     return send_sysex(sx, p);
 }
@@ -294,12 +302,14 @@ int send_amp_end(void)
 
 /* ---- outbound: Chlorine ---- */
 
-int send_cl_start(uint32_t num_points)
+int send_cl_start(uint32_t num_points, uint32_t ts_ms, uint16_t meas_id)
 {
-    uint8_t sx[10];
+    uint8_t sx[18];
     uint16_t p = 0;
     sx[p++] = 0xF0; sx[p++] = 0x7D; sx[p++] = RSP_CL_START;
     encode_u16((uint16_t)num_points, &sx[p]); p += 3;
+    encode_u32(ts_ms, &sx[p]); p += 5;
+    encode_u16(meas_id, &sx[p]); p += 3;
     sx[p++] = 0xF7;
     return send_sysex(sx, p);
 }
@@ -349,14 +359,17 @@ int send_ph_cal(float slope, float offset)
 
 /* ---- outbound: pH ---- */
 
-int send_ph_result(float v_ocp_mv, float ph, float temp_c)
+int send_ph_result(float v_ocp_mv, float ph, float temp_c,
+                   uint32_t ts_ms, uint16_t meas_id)
 {
-    uint8_t sx[20];
+    uint8_t sx[28];
     uint16_t p = 0;
     sx[p++] = 0xF0; sx[p++] = 0x7D; sx[p++] = RSP_PH_RESULT;
     encode_float(v_ocp_mv, &sx[p]); p += 5;
     encode_float(ph, &sx[p]); p += 5;
     encode_float(temp_c, &sx[p]); p += 5;
+    encode_u32(ts_ms, &sx[p]); p += 5;
+    encode_u16(meas_id, &sx[p]); p += 3;
     sx[p++] = 0xF7;
     return send_sysex(sx, p);
 }
diff --git a/main/protocol.h b/main/protocol.h
index c040c3d..f13134c 100644
--- a/main/protocol.h
+++ b/main/protocol.h
@@ -113,29 +113,32 @@ float    decode_float(const uint8_t *d);
 uint16_t decode_u16(const uint8_t *d);
 
 /* outbound: EIS */
-int send_sweep_start(uint32_t num_points, float freq_start, float freq_stop);
+int send_sweep_start(uint32_t num_points, float freq_start, float freq_stop,
+                     uint32_t ts_ms, uint16_t meas_id);
 int send_eis_point(uint16_t index, const EISPoint *pt);
 int send_sweep_end(void);
 int send_config(const EISConfig *cfg);
 
 /* outbound: LSV */
-int send_lsv_start(uint32_t num_points, float v_start, float v_stop);
+int send_lsv_start(uint32_t num_points, float v_start, float v_stop,
+                   uint32_t ts_ms, uint16_t meas_id);
 int send_lsv_point(uint16_t index, float v_mv, float i_ua);
 int send_lsv_end(void);
 
 /* outbound: Amperometry */
-int send_amp_start(float v_hold);
+int send_amp_start(float v_hold, uint32_t ts_ms, uint16_t meas_id);
 int send_amp_point(uint16_t index, float t_ms, float i_ua);
 int send_amp_end(void);
 
 /* outbound: Chlorine */
-int send_cl_start(uint32_t num_points);
+int send_cl_start(uint32_t num_points, uint32_t ts_ms, uint16_t meas_id);
 int send_cl_point(uint16_t index, float t_ms, float i_ua, uint8_t phase);
 int send_cl_result(float i_free_ua, float i_total_ua);
 int send_cl_end(void);
 
 /* outbound: pH */
-int send_ph_result(float v_ocp_mv, float ph, float temp_c);
+int send_ph_result(float v_ocp_mv, float ph, float temp_c,
+                   uint32_t ts_ms, uint16_t meas_id);
 
 /* outbound: temperature */
 int send_temp(float temp_c);