diff --git a/PDP10/kx10_cpu.c b/PDP10/kx10_cpu.c
index 0c2f5567..a9f3ec1d 100644
--- a/PDP10/kx10_cpu.c
+++ b/PDP10/kx10_cpu.c
@@ -10108,6 +10108,7 @@ for(i=0; i < 128; dev_irq[i++] = 0);
 sim_brk_types = SWMASK('E') | SWMASK('W') | SWMASK('R');
 sim_brk_dflt = SWMASK ('E');
 sim_clock_precalibrate_commands = pdp10_clock_precalibrate_commands;
+sim_vm_initial_ips = 4 * SIM_INITIAL_IPS;
 sim_rtcn_init_unit (&cpu_unit[0], cpu_unit[0].wait, TMR_RTC);
 sim_activate(&cpu_unit[0], 10000);
 #if MPX_DEV
diff --git a/PDP10/pdp10_cpu.c b/PDP10/pdp10_cpu.c
index a37c8070..667199e2 100644
--- a/PDP10/pdp10_cpu.c
+++ b/PDP10/pdp10_cpu.c
@@ -2380,6 +2380,7 @@ if (M == NULL)
 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;
+sim_vm_initial_ips = 2 * SIM_INITIAL_IPS;
 pcq_r = find_reg ("PCQ", NULL, dptr);
 if (pcq_r)
     pcq_r->qptr = 0;
diff --git a/PDP8/pdp8_cpu.c b/PDP8/pdp8_cpu.c
index 30782b78..3b1990df 100644
--- a/PDP8/pdp8_cpu.c
+++ b/PDP8/pdp8_cpu.c
@@ -1378,9 +1378,11 @@ return reason;
  */
 
 static const char *pdp8_clock_precalibrate_commands[] = {
-    "-m 100 ISZ 110",
-    "-m 101 JMP 100",
-    "-m 102 JMP 100",
+    "106 100"
+    "-m 100 MQL MQA"
+    "-m 101 ISZ 112",
+    "-m 102 JMP I 106",
+    "-m 103 JMP I 106",
     "PC 100",
     NULL};
 
@@ -1398,6 +1400,7 @@ if (pcq_r)
 else 
     return SCPE_IERR;
 sim_clock_precalibrate_commands = pdp8_clock_precalibrate_commands;
+sim_vm_initial_ips = 10 * SIM_INITIAL_IPS;
 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 125d8475..b68cc72e 100644
--- a/VAX/vax_cpu.c
+++ b/VAX/vax_cpu.c
@@ -3319,6 +3319,7 @@ 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;
+    sim_vm_initial_ips = SIM_INITIAL_IPS;
     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 725ff299..b3aa2fca 100644
Binary files a/doc/simh.doc and b/doc/simh.doc differ
diff --git a/scp.h b/scp.h
index ba2db861..3e2b1435 100644
--- a/scp.h
+++ b/scp.h
@@ -429,6 +429,7 @@ 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;
+extern int32 sim_vm_initial_ips;                        /* base estimate of simulated instructions per second */
 extern const char *sim_vm_interval_units;               /* Simulator can change this - default "instructions" */
 extern const char *sim_vm_step_unit;                    /* Simulator can change this - default "instruction" */
 
diff --git a/sim_timer.c b/sim_timer.c
index 8dd4cf07..3fe6d119 100644
--- a/sim_timer.c
+++ b/sim_timer.c
@@ -150,6 +150,8 @@ return real_sim_os_ms_sleep (msec);
 t_bool sim_idle_enab = FALSE;                       /* global flag */
 volatile t_bool sim_idle_wait = FALSE;              /* global flag */
 
+int32 sim_vm_initial_ips = SIM_INITIAL_IPS;
+
 static int32 sim_precalibrate_ips = SIM_INITIAL_IPS;
 static int32 sim_calb_tmr = -1;                     /* the system calibrated timer */
 static int32 sim_calb_tmr_last = -1;                /* shadow value when at sim> prompt */
@@ -3471,7 +3473,7 @@ sim_idle_stable = 0;
 double 
 sim_host_speed_factor (void)
 {
-if (sim_precalibrate_ips > SIM_INITIAL_IPS)
+if (sim_precalibrate_ips > sim_vm_initial_ips)
     return 1.0;
-return (double)SIM_INITIAL_IPS / (double)sim_precalibrate_ips;
+return (double)sim_vm_initial_ips / (double)sim_precalibrate_ips;
 }