diff --git a/PDP10/kx10_cpu.c b/PDP10/kx10_cpu.c
index c3863f0ac..2d51230ab 100644
--- a/PDP10/kx10_cpu.c
+++ b/PDP10/kx10_cpu.c
@@ -781,7 +781,7 @@ DEVICE cpu_dev = {
 #if PIDP10
                         /* Update MI register if address matches */
 #define UPDATE_MI(a)    if (!MI_flag && a == AS) { \
-	                     MI = MB; \
+                             MI = MB; \
                         }
 #else
 #define UPDATE_MI(a)
@@ -2331,7 +2331,7 @@ int Mem_write(int flag, int cur_context) {
             if (sim_brk_summ && sim_brk_test(last_addr, SWMASK('W')))
                 watch_stop = 1;
             M[last_addr] = MB;
-	        UPDATE_MI(last_addr);
+            UPDATE_MI(last_addr);
             modify = 0;
             return 0;
         }
diff --git a/sim_card.c b/sim_card.c
index d107273fa..09e942bc2 100644
--- a/sim_card.c
+++ b/sim_card.c
@@ -33,9 +33,11 @@
                 First characters 6789----
                 Second character 21012345
                                  111
-                Top 4 bits of second character are 0.
-                It is unlikely that any other format could
-                look like this.
+                The lower order 4 bits of first word are all
+                zero. It is unlikely that any other format could
+                look like this. An ASCII card could match this
+                if it is all blank, but the trailing return would
+                cause it to fail this test.
 
         BCD Format:
                 Each record variable length (80 chars or less).
diff --git a/sim_card.h b/sim_card.h
index c29cec4d4..19fdd0254 100644
--- a/sim_card.h
+++ b/sim_card.h
@@ -30,12 +30,15 @@
 
         Binary Card format:
                 Each record 160 characters.
-                First character   21012345
-                                  111
-                Second characters 6789----
-                Top 4 bits of second character are 0.
-                It is unlikely that ascii text or BCD format
-                text could produce similar profile.
+                First characters 6789----
+                Second character 21012345
+                                 111
+
+                The lower order 4 bits of first word are all
+                zero. It is unlikely that any other format could
+                look like this. An ASCII card could match this
+                if it is all blank, but the trailing return would
+                cause it to fail this test.
 
         BCD Format:
                 Each record variable length (80 chars or less).