diff --git a/src/include/pv-internal.h b/src/include/pv-internal.h
index ba9830c..d7f6491 100644
--- a/src/include/pv-internal.h
+++ b/src/include/pv-internal.h
@@ -201,6 +201,9 @@ struct pvstate_s {
 		off_t size;                      /* total size of data */
 		unsigned int skip_errors;        /* skip read errors counter */
 		int output_fd;                   /* fd to write output to */
+		pid_t othermonitor_pid;		 /* pid of the other monitor, in "-M both" mode */
+		int othermonitor_read_fd;	 /* fd to read transfer counts from other monitor */
+		int othermonitor_write_fd;	 /* fd to write transfer counts to other monitor */
 		unsigned int average_rate_window; /* time window in seconds for average rate calculations */
 		unsigned int history_interval;	 /* seconds between each average rate calc history entry */
 		pvdisplay_width_t width;         /* screen width */
diff --git a/src/include/pv.h b/src/include/pv.h
index c7690c0..a8009ab 100644
--- a/src/include/pv.h
+++ b/src/include/pv.h
@@ -239,6 +239,7 @@ extern void pv_state_extra_display_set(pvstate_t, /*@null@*/ const char *);
 extern void pv_state_output_set(pvstate_t, int, const char *);
 extern void pv_state_average_rate_window_set(pvstate_t, unsigned int);
 extern void pv_state_set_terminal_supports_utf8(pvstate_t, bool);
+extern void pv_state_othermonitor_set(pvstate_t, pid_t, int, int);
 
 extern void pv_state_inputfiles(pvstate_t, unsigned int, const char **);
 extern void pv_state_watchfds(pvstate_t, unsigned int, const pid_t *, const int *);
diff --git a/src/main/main.c b/src/main/main.c
index 7429f60..67e4a20 100644
--- a/src/main/main.c
+++ b/src/main/main.c
@@ -286,14 +286,7 @@ static int pv__store_and_forward(pvstate_t state, opts_t opts, bool can_have_eta
  * As a side effect, "command_fd" is closed.
  */
 static int pv__run_monitor(const char *program_name, pvstate_t state, pvside_t side, int command_fd,
-			   /*@unused@ */
-			   __attribute__((unused)) pid_t othermonitor_pid,
-			   /*@unused@ */
-			   __attribute__((unused))
-			   int othermonitor_read_fd,
-			   /*@unused@ */
-			   __attribute__((unused))
-			   int othermonitor_write_fd)
+			   pid_t othermonitor_pid, int othermonitor_read_fd, int othermonitor_write_fd)
 {
 	const char *dummy_argv[1];	 /* flawfinder: ignore */
 
@@ -325,7 +318,7 @@ static int pv__run_monitor(const char *program_name, pvstate_t state, pvside_t s
 		fprintf(stderr, "%s: %s\n", program_name, strerror(errno));
 	}
 
-	/* TODO: pass othermonitor_* into the state for ratio display. */
+	pv_state_othermonitor_set(state, othermonitor_pid, othermonitor_read_fd, othermonitor_write_fd);
 
 	/*@-observertrans@ */
 	dummy_argv[0] = "-";
diff --git a/src/main/options.c b/src/main/options.c
index ead226e..cf85a6f 100644
--- a/src/main/options.c
+++ b/src/main/options.c
@@ -1290,6 +1290,7 @@ opts_t opts_parse(unsigned int argc, char **argv)
 		opts->eta = true;
 		opts->rate = true;
 		opts->bytes = true;
+		/* TODO: add ratio format if "-M both" */
 	}
 
 	/* If -Z was given but not -E, pretend one -E was given too. */
diff --git a/src/pv/display.c b/src/pv/display.c
index 2c7a1ff..365b9b0 100644
--- a/src/pv/display.c
+++ b/src/pv/display.c
@@ -544,6 +544,7 @@ pvdisplay_bytecount_t pv_formatter_segmentcontent(char *content, pvformatter_arg
 		{ "{sgr:colour,...}", &pv_formatter_sgr, false },
 		{ NULL, NULL, false }
 	};
+	/* TODO: formatter for ratio, for "-M both" */
 	return format_component_array;
 }
 
diff --git a/src/pv/loop.c b/src/pv/loop.c
index 776c832..5c82bc9 100644
--- a/src/pv/loop.c
+++ b/src/pv/loop.c
@@ -185,6 +185,10 @@ int pv_main_loop(pvstate_t state)
 	unsigned int file_idx;
 	bool output_is_pipe;
 
+	/* TODO: treat "-F ''" as "-q" so there's no extra blank line. */
+	/* TODO: if "-q", turn off "-c", again so there's no blank line. */
+	/* May need local no_display and cursor flags for this. */
+
 	/*
 	 * "written" is ALWAYS bytes written by the last transfer.
 	 *
@@ -338,6 +342,9 @@ int pv_main_loop(pvstate_t state)
 			pv_elapsedtime_add_nsec(&next_remotecheck, REMOTE_INTERVAL);
 		}
 
+		/* TODO: occasionally check othermonitor_read_fd, calculate ratio */
+		/* TODO: occasionally send to othermonitor_write_fd */
+
 		if (1 == state->flags.trigger_exit)
 			break;
 
diff --git a/src/pv/state.c b/src/pv/state.c
index 2345576..81cba2c 100644
--- a/src/pv/state.c
+++ b/src/pv/state.c
@@ -191,6 +191,9 @@ pvstate_t pv_state_alloc(void)
 
 	state->watchfd.count = 0;
 	state->control.output_fd = -1;
+	state->control.othermonitor_pid = 0;
+	state->control.othermonitor_read_fd = -1;
+	state->control.othermonitor_write_fd = -1;
 #ifdef HAVE_IPC
 	state->cursor.shmid = -1;
 	state->cursor.pvcount = 1;
@@ -769,6 +772,13 @@ void pv_state_set_terminal_supports_utf8(pvstate_t state, bool val)
 	state->status.terminal_supports_utf8 = val;
 }
 
+void pv_state_othermonitor_set(pvstate_t state, pid_t pid, int read_fd, int write_fd)
+{
+	state->control.othermonitor_pid = pid;
+	state->control.othermonitor_read_fd = read_fd;
+	state->control.othermonitor_write_fd = write_fd;
+}
+
 /*
  * Set the array of input files.
  */