diff --git a/ocat.c b/ocat.c
index c4f4bf3..616a0d0 100644
--- a/ocat.c
+++ b/ocat.c
@@ -75,17 +75,17 @@ void usage(char *prog)
 	printf("Usage: %s [options..] [file ...]\n", prog);
 	printf("  --help		-h	this message\n");
 	printf("  --list		-l	list users (or a user's (-u) devices\n");
-	printf("  --user username	-u	specify username\n");
-	printf("  --device devicename   -d	specify device name\n");
-	printf("  --from <time>         -F      from date/time\n");
-	printf("  --to   <time>         -T      to date/time\n");
+	printf("  --user username	-u	specify username ($OCAT_USERNAME)\n");
+	printf("  --device devicename   -d	specify device name ($OCAT_DEVICE)\n");
+	printf("  --from <time>         -F      from date/time; default -6H\n");
+	printf("  --to   <time>         -T      to date/time; default now\n");
 	printf("         specify <time> as     YYYY-MM-DDTHH:MM:SS\n");
 	printf("                               YYYY-MM-DDTHH:MM\n");
 	printf("                               YYYY-MM-DDTHH\n");
 	printf("                               YYYY-MM-DD\n");
 	printf("                               YYYY-MM\n");
 	printf("  --format json    	-f     output format (default: JSON)\n");
-	printf("           csv\n");
+	printf("           csv                 (overrides $OCAT_FORMAT\n");
 	printf("           geojson\n");
 	printf("           raw\n");
 	printf("           tabular\n");