diff --git a/PDP10/pdp10_cpu.c b/PDP10/pdp10_cpu.c
index 9262f11b..30b8bb50 100644
--- a/PDP10/pdp10_cpu.c
+++ b/PDP10/pdp10_cpu.c
@@ -2347,6 +2347,19 @@ pi_eval ();                                             /* eval pi system */
 return;
 }
 
+/*
+ * This sequence of instructions is a mix that hopefully
+ * represents a resonable instruction set that is a close 
+ * estimate to the normal calibrated result.
+ */
+
+static const char *pdp10_clock_precalibrate_commands[] = {
+    "-m 100 ADDM 0,110",
+    "-m 101 ADDI 0,1",
+    "-m 102 JRST 100",
+    "PC 100",
+    NULL};
+
 /* Reset routine */
 
 t_stat cpu_reset (DEVICE *dptr)
@@ -2368,10 +2381,12 @@ if (M == NULL)
     return SCPE_MEM;
 sim_vm_pc_value = &pdp10_pc_value;
 sim_vm_is_subroutine_call = &cpu_is_pc_a_subroutine_call;
+sim_clock_precalibrate_commands = pdp10_clock_precalibrate_commands;
 pcq_r = find_reg ("PCQ", NULL, dptr);
 if (pcq_r)
     pcq_r->qptr = 0;
-else return SCPE_IERR;
+else
+    return SCPE_IERR;
 sim_brk_types = sim_brk_dflt = SWMASK ('E');
 return SCPE_OK;
 }
diff --git a/PDP11/pdp11_cpu.c b/PDP11/pdp11_cpu.c
index 293995fb..19525e55 100644
--- a/PDP11/pdp11_cpu.c
+++ b/PDP11/pdp11_cpu.c
@@ -3338,6 +3338,19 @@ else if (CPUT (HAS_STKLR)) {                            /* register limit? */
 return;                                                 /* no stack limit */
 }
 
+/*
+ * This sequence of instructions is a mix that mimics
+ * a resonable instruction set that is a close estimate
+ * to the normal calibrated result.
+ */
+
+static const char *pdp11_clock_precalibrate_commands[] = {
+    "-m 100 INC 120",
+    "-m 104 INC 122",
+    "-m 110 BR  100",
+    "PC 100",
+    NULL};
+
 /* Reset routine */
 
 t_stat cpu_reset (DEVICE *dptr)
@@ -3365,6 +3378,7 @@ if (M == NULL) {                    /* First time init */
                     SWMASK ('W')|SWMASK ('X');
     sim_brk_type_desc = cpu_breakpoints;
     sim_vm_is_subroutine_call = &cpu_is_pc_a_subroutine_call;
+    sim_clock_precalibrate_commands = pdp11_clock_precalibrate_commands;
     auto_config(NULL, 0);           /* do an initial auto configure */
     }
 pcq_r = find_reg ("PCQ", NULL, dptr);
diff --git a/PDP8/pdp8_cpu.c b/PDP8/pdp8_cpu.c
index aca02045..30782b78 100644
--- a/PDP8/pdp8_cpu.c
+++ b/PDP8/pdp8_cpu.c
@@ -1371,6 +1371,19 @@ pcq_r->qptr = pcq_p;                                    /* update pc q ptr */
 return reason;
 }                                                       /* end sim_instr */
 
+/*
+ * This sequence of instructions is a mix that hopefully
+ * represents a resonable instruction set that is a close 
+ * estimate to the normal calibrated result.
+ */
+
+static const char *pdp8_clock_precalibrate_commands[] = {
+    "-m 100 ISZ 110",
+    "-m 101 JMP 100",
+    "-m 102 JMP 100",
+    "PC 100",
+    NULL};
+
 /* Reset routine */
 
 t_stat cpu_reset (DEVICE *dptr)
@@ -1382,7 +1395,9 @@ UF = UB = gtf = emode = 0;
 pcq_r = find_reg ("PCQ", NULL, dptr);
 if (pcq_r)
     pcq_r->qptr = 0;
-else return SCPE_IERR;
+else 
+    return SCPE_IERR;
+sim_clock_precalibrate_commands = pdp8_clock_precalibrate_commands;
 sim_brk_types = SWMASK ('E') | SWMASK('I');
 sim_brk_dflt = SWMASK ('E');
 return SCPE_OK;
diff --git a/VAX/vax_cpu.c b/VAX/vax_cpu.c
index 73058c86..df29b086 100644
--- a/VAX/vax_cpu.c
+++ b/VAX/vax_cpu.c
@@ -3284,6 +3284,21 @@ void cpu_idle (void)
 sim_idle (TMR_CLK, TRUE);
 }
 
+/*
+ * This sequence of instructions is a mix that mimics
+ * a resonable instruction set that is a close estimate
+ * to the calibrated result without a direct "loop to 
+ * self" instruction that would halt simulation.
+ */
+
+static const char *vax_clock_precalibrate_commands[] = {
+    "-m 100 INCL  120",
+    "-m 103 INCL  124",
+    "-m 106 MULL3 120,124,128",
+    "-m 10D BRW   100",
+    "PC 100",
+    NULL};
+
 /* Reset */
 
 t_stat cpu_reset (DEVICE *dptr)
@@ -3299,6 +3314,7 @@ FLUSH_ISTR;                             /* init I-stream */
 if (M == NULL) {                        /* first time init? */
     sim_brk_types = sim_brk_dflt = SWMASK ('E');
     sim_vm_is_subroutine_call = cpu_is_pc_a_subroutine_call;
+    sim_clock_precalibrate_commands = vax_clock_precalibrate_commands;
     pcq_r = find_reg ("PCQ", NULL, dptr);
     if (pcq_r == NULL)
         return SCPE_IERR;
diff --git a/doc/simh.doc b/doc/simh.doc
index 96c4c1b9..43dd3652 100644
Binary files a/doc/simh.doc and b/doc/simh.doc differ
diff --git a/scp.c b/scp.c
index 7781648a..3523cacf 100644
--- a/scp.c
+++ b/scp.c
@@ -451,6 +451,8 @@ t_addr (*sim_vm_parse_addr) (DEVICE *dptr, CONST char *cptr, CONST char **tptr)
 t_value (*sim_vm_pc_value) (void) = NULL;
 t_bool (*sim_vm_is_subroutine_call) (t_addr **ret_addrs) = NULL;
 t_bool (*sim_vm_fprint_stopped) (FILE *st, t_stat reason) = NULL;
+const char **sim_clock_precalibrate_commands = NULL;
+
 
 /* Prototypes */
 
@@ -2594,6 +2596,7 @@ if (!sim_quiet) {
     printf ("\n");
     show_version (stdout, NULL, NULL, 0, NULL);
     }
+sim_timer_precalibrate_execution_rate ();
 show_version (stdnul, NULL, NULL, 1, NULL);             /* Quietly set SIM_OSTYPE */
 #if defined (HAVE_PCREPOSIX_H)
 setenv ("SIM_REGEX_TYPE", "PCREPOSIX", 1);              /* Publish regex type */
diff --git a/scp.h b/scp.h
index d9c5cc5f..c335e8a8 100644
--- a/scp.h
+++ b/scp.h
@@ -420,6 +420,8 @@ extern t_addr (*sim_vm_parse_addr) (DEVICE *dptr, CONST char *cptr, CONST char *
 extern t_bool (*sim_vm_fprint_stopped) (FILE *st, t_stat reason);
 extern t_value (*sim_vm_pc_value) (void);
 extern t_bool (*sim_vm_is_subroutine_call) (t_addr **ret_addrs);
+extern const char **sim_clock_precalibrate_commands;
+
 
 /* Core SCP libraries can potentially have unit test routines.
    These defines help implement consistent unit test functionality */
diff --git a/sim_timer.c b/sim_timer.c
index ce6e8ed3..39d9f617 100644
--- a/sim_timer.c
+++ b/sim_timer.c
@@ -788,6 +788,7 @@ t_stat sim_throt_svc (UNIT *uptr);
 t_stat sim_timer_tick_svc (UNIT *uptr);
 t_stat sim_timer_stop_svc (UNIT *uptr);
 
+
 #define DBG_IDL       TIMER_DBG_IDLE        /* idling */
 #define DBG_QUE       TIMER_DBG_QUEUE       /* queue activities */
 #define DBG_MUX       TIMER_DBG_MUX         /* tmxr queue activities */
@@ -3209,3 +3210,47 @@ void sim_set_rom_delay_factor (uint32 delay)
 {
 sim_rom_delay = delay;
 }
+
+/* sim_timer_precalibrate_execution_rate
+ *
+ * The point of this routine is to run a bunch of simulator provided
+ * instructions that don't do anything, but run in an effective loop.
+ * That loop is run for some 5 million instructions and based on 
+ * the time those 5 million instructions take to execute the effective
+ * execution rate.  That rate is used to avoid the initial 3 to 5 
+ * seconds that normal clock calibration takes.
+ *
+ */
+void sim_timer_precalibrate_execution_rate (void)
+{
+const char **cmd = sim_clock_precalibrate_commands;
+uint32 start, end;
+double ips_rate;
+int32 saved_switches = sim_switches;
+int32 tmr;
+UNIT precalib_unit = { UDATA (&sim_timer_stop_svc, 0, 0) };
+
+if (cmd == NULL)
+    return;
+sim_run_boot_prep (RU_GO);
+while (sim_clock_queue != QUEUE_LIST_END)
+    sim_cancel (sim_clock_queue);
+while (*cmd)
+     exdep_cmd (EX_D, *(cmd++));
+sim_switches = saved_switches;
+sim_cancel (&SIM_INTERNAL_UNIT);
+sim_activate (&precalib_unit, SIM_INITIAL_IPS);
+start = sim_os_msec();
+sim_instr();
+end = sim_os_msec();
+ips_rate = 1000.0 * (SIM_INITIAL_IPS / (double)(end - start));
+
+for (tmr=0; tmr<=SIM_NTIMERS; tmr++) {
+    if (rtc_hz[tmr])
+        rtc_initd[tmr] = rtc_currd[tmr] = (int32)(ips_rate / rtc_hz[tmr]);
+    }
+reset_all_p (0);
+sim_run_boot_prep (RU_GO);
+if (sim_switches & SWMASK ('V'))
+    sim_printf ("Pre-Calibrate execution rate: %s cycles/sec\n", sim_fmt_numeric (ips_rate));
+}
diff --git a/sim_timer.h b/sim_timer.h
index 59226fef..0ec85b89 100644
--- a/sim_timer.h
+++ b/sim_timer.h
@@ -76,7 +76,7 @@ int clock_gettime(int clock_id, struct timespec *tp);
 #define SIM_NTIMERS     8                           /* # timers */
 #define SIM_TMAX        500                         /* max timer makeup */
 
-#define SIM_INITIAL_IPS 500000                      /* uncalibrated assumption */
+#define SIM_INITIAL_IPS 5000000                     /* uncalibrated assumption */
                                                     /* about instructions per second */
 
 #define SIM_IDLE_CAL    10                          /* ms to calibrate */
@@ -145,6 +145,7 @@ t_stat sim_clock_coschedule_abs (UNIT *uptr, int32 interval);
 t_stat sim_clock_coschedule_tmr (UNIT *uptr, int32 tmr, int32 ticks);
 t_stat sim_clock_coschedule_tmr_abs (UNIT *uptr, int32 tmr, int32 ticks);
 double sim_timer_inst_per_sec (void);
+void sim_timer_precalibrate_execution_rate (void);
 int32 sim_rtcn_tick_size (int32 tmr);
 int32 sim_rtcn_calibrated_tmr (void);
 t_bool sim_timer_idle_capable (uint32 *host_ms_sleep_1, uint32 *host_tick_ms);