diff --git a/NANOVNA_STM32_F072/rtc_v2.c b/NANOVNA_STM32_F072/rtc_v2.c
index f6df158..68deac0 100644
--- a/NANOVNA_STM32_F072/rtc_v2.c
+++ b/NANOVNA_STM32_F072/rtc_v2.c
@@ -149,7 +149,9 @@ void rtc_init(void){
   // If calendar has not been initialized yet then proceed with the initial setup.
   if ((RTC->ISR & RTC_ISR_INITS) == 0 || RTC->PRER != rtc_prer) {
     if (rtc_enter_init()){
-      RTC->CR   &= ~RTC_CR_COE;
+      RTC->CR   = 0
+//              | RTC_CR_COSEL    // RTC output 1Hz (or 512Hz if disabled)
+                 ;
       RTC->ISR  = RTC_ISR_INIT;     // Clearing all but RTC_ISR_INIT.
       RTC->PRER = rtc_prer;         // Prescaler value loaded in registers 2 times
       RTC->PRER = rtc_prer;
@@ -162,14 +164,10 @@ void rtc_init(void){
 }
 
 void rtc_set_cal(float ppm) {
-  ppm*= (1<<20) / 1000000.0f;
-  int32_t cal = ppm > 0 ? ppm + 0.5f : ppm - 0.5f;
-  if ((RTC->ISR & RTC_ISR_RECALPF) != 0 || cal < -511 || cal > 512)
+  int32_t cal = ppm * (1<<20) / 1000000.0f + 511.5f;
+  if ((RTC->ISR & RTC_ISR_RECALPF) || (uint32_t)cal > 1024)
     return;
-  if (cal > 0)
-    RTC->CALR = RTC_CALR_CALP | (512 - cal);
-  else
-    RTC->CALR = -cal;
+  RTC->CALR = (511 - cal) & (RTC_CALR_CALP | RTC_CALR_CALM);
 }
 
 float rtc_get_cal(void) {
diff --git a/NANOVNA_STM32_F303/rtc_v2.c b/NANOVNA_STM32_F303/rtc_v2.c
index f6df158..bf5fe27 100644
--- a/NANOVNA_STM32_F303/rtc_v2.c
+++ b/NANOVNA_STM32_F303/rtc_v2.c
@@ -149,7 +149,9 @@ void rtc_init(void){
   // If calendar has not been initialized yet then proceed with the initial setup.
   if ((RTC->ISR & RTC_ISR_INITS) == 0 || RTC->PRER != rtc_prer) {
     if (rtc_enter_init()){
-      RTC->CR   &= ~RTC_CR_COE;
+      RTC->CR   = 0
+//              | RTC_CR_COSEL    // RTC output 1Hz (or 512Hz if disabled)
+                 ;
       RTC->ISR  = RTC_ISR_INIT;     // Clearing all but RTC_ISR_INIT.
       RTC->PRER = rtc_prer;         // Prescaler value loaded in registers 2 times
       RTC->PRER = rtc_prer;
@@ -162,14 +164,10 @@ void rtc_init(void){
 }
 
 void rtc_set_cal(float ppm) {
-  ppm*= (1<<20) / 1000000.0f;
-  int32_t cal = ppm > 0 ? ppm + 0.5f : ppm - 0.5f;
-  if ((RTC->ISR & RTC_ISR_RECALPF) != 0 || cal < -511 || cal > 512)
+  int32_t cal = ppm * (1<<20) / 1000000.0f + 511.5f;
+  if ((RTC->ISR & RTC_ISR_RECALPF) || (uint32_t)cal > 1024)
     return;
-  if (cal > 0)
-    RTC->CALR = RTC_CALR_CALP | (512 - cal);
-  else
-    RTC->CALR = -cal;
+  RTC->CALR = ((511 - cal) & (RTC_CALR_CALP | RTC_CALR_CALM));
 }
 
 float rtc_get_cal(void) {
diff --git a/main.c b/main.c
index 67feddf..b5c1231 100644
--- a/main.c
+++ b/main.c
@@ -125,7 +125,7 @@ static uint16_t p_sweep = 0;
 float measured[2][SWEEP_POINTS_MAX][2];
 
 #undef VERSION
-#define VERSION "1.2.28"
+#define VERSION "1.2.29"
 
 // Version text, displayed in Config->Version menu, also send by info command
 const char *info_about[]={
@@ -772,7 +772,7 @@ VNA_SHELL_FUNCTION(cmd_time)
   dt_buf[0] = rtc_get_tr_bcd(); // TR should be read first for sync
   dt_buf[1] = rtc_get_dr_bcd(); // DR should be read second
   static const uint8_t idx_to_time[] = {6,5,4,2,  1,  0};
-  static const char       time_cmd[] = "y|m|d|h|min|sec";
+  static const char       time_cmd[] = "y|m|d|h|min|sec|ppm";
   //            0    1   2       4      5     6
   // time[] ={sec, min, hr, 0, day, month, year, 0}
   uint8_t   *time = (uint8_t*)dt_buf;
@@ -782,6 +782,10 @@ VNA_SHELL_FUNCTION(cmd_time)
   }
   if (argc!=2) goto usage;
   int idx = get_str_index(argv[0], time_cmd);
+  if(idx == 6) {
+    rtc_set_cal(my_atof(argv[1]));
+    return;
+  }
   uint32_t val = my_atoui(argv[1]);
   if (idx < 0 || val > 99)
     goto usage;
diff --git a/ui.c b/ui.c
index 29e8ec7..662daab 100644
--- a/ui.c
+++ b/ui.c
@@ -2306,8 +2306,8 @@ static UI_FUNCTION_ADV_CALLBACK(menu_rtc_out_acb)
 }
 
 const menuitem_t menu_rtc_cal[] = {
-  { MT_ADV_CALLBACK, KM_RTC_CAL,   "RTC CAL\n " R_LINK_COLOR "%b.4f " S_PPM,   menu_keyboard_acb },
-  { MT_ADV_CALLBACK, 0,            "RTC OUT\n%s"   ,                           menu_rtc_out_acb },
+  { MT_ADV_CALLBACK, KM_RTC_CAL,   "RTC CAL\n" R_LINK_COLOR "%+b.4f" S_PPM, menu_keyboard_acb },
+  { MT_ADV_CALLBACK, 0,            "RTC OUT\n%s"   ,                        menu_rtc_out_acb },
   { MT_NEXT, 0, NULL, menu_back } // next-> menu_back
 };
 #endif