diff --git a/eeshow/Makefile b/eeshow/Makefile
index 6323f05..b7bf9ae 100644
--- a/eeshow/Makefile
+++ b/eeshow/Makefile
@@ -13,7 +13,7 @@
 NAME = eeshow
 OBJS = main.o sch-parse.o sch-render.o lib-parse.o lib-render.o \
        gui.o gui-over.o gui-aoi.o fmt-pango.o \
-       file.o git-util.o git-file.o git-hist.o \
+       file.o git-util.o git-file.o git-hist.o delta.o \
        style.o fig.o record.o cro.o diff.o gfx.o dwg.o text.o misc.o
 
 CFLAGS = -g  -Wall -Wextra -Wno-unused-parameter -Wshadow \
diff --git a/eeshow/delta.c b/eeshow/delta.c
new file mode 100644
index 0000000..3c5639b
--- /dev/null
+++ b/eeshow/delta.c
@@ -0,0 +1,246 @@
+/*
+ * delta.c - Find differences in .sch files
+ *
+ * Written 2016 by Werner Almesberger
+ * Copyright 2016 by Werner Almesberger
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+
+#include <stddef.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "util.h"
+#include "text.h"
+#include "sch.h"
+#include "delta.h"
+
+
+/*
+ * @@@ we should clone components and compare them, too
+ *
+ * if two components or sub-sheets mismatch in their field lists, we should
+ * remove matching items from the lists.
+ *
+ * @@@@ line(A, B) == line(B, A), etc.
+ */
+
+static struct sch_obj *objs_clone(const struct sch_obj *objs)
+{
+	struct sch_obj *new_objs = NULL;
+	struct sch_obj **next = &new_objs;
+	const struct sch_obj *obj;
+
+	for (obj = objs; obj; obj = obj->next) {
+		*next = alloc_type(struct sch_obj);
+		**next = *obj;
+		next = &(*next)->next;
+	}
+	*next = NULL;
+	return new_objs;
+}
+
+
+static void add_obj(struct sheet *sch, struct sch_obj *obj)
+{
+	*sch->next_obj = obj;
+	sch->next_obj = &obj->next;
+	obj->next = NULL;
+}
+
+
+static bool comp_fields_eq(const struct comp_field *a,
+    const struct comp_field *b)
+{
+	while (a && b) {
+		if (a->txt.x != b->txt.x || a->txt.y != b->txt.y)
+			return 0;
+		if (a->txt.size != b->txt.size)
+			return 0;
+		if (a->txt.rot != b->txt.rot)
+			return 0;
+		if (a->txt.hor != b->txt.hor || a->txt.vert != b->txt.vert)
+			return 0;
+		if (strcmp(a->txt.s, b->txt.s))
+			return 0;
+		a = a->next;
+		b = b->next;
+	}
+	return a == b;
+}
+
+
+static bool sheet_fields_eq(const struct sheet_field *a,
+    const struct sheet_field *b)
+{
+	const struct sheet_field *ta = a;
+	const struct sheet_field *tb = b;
+
+	for (ta = a; ta; ta = ta->next) {
+		for (tb = b; tb; tb = tb->next) {
+			if (ta->x != tb->x || ta->y != tb->y)
+				continue;
+			if (ta->dim != tb->dim)
+				continue;
+			if (ta->dim != tb->dim)
+				continue;
+			if (ta->shape != tb->shape)
+				continue;
+			if (strcmp(ta->s, tb->s))
+				continue;
+			goto match;
+		}
+		return 0;
+match:
+		continue;
+	}
+
+	while (a && b) {
+		a = a->next;
+		b = b->next;
+	}
+	return a == b;
+}
+
+
+/*
+ * @@@ idea: if we send all strings through a "unique" function, we can
+ * memcmp things like "struct sch_text" without having to go through the
+ * fields individually.
+ */
+
+static bool obj_eq(const struct sch_obj *a, const struct sch_obj *b)
+{
+	if (a->type != b->type)
+		return 0;
+	if (a->x != b->x || a->y != b->y)
+		return 0;
+	switch (a->type) {
+	case sch_obj_wire:
+		if (a->u.wire.fn != b->u.wire.fn)
+			return 0;
+		if (a->x != b->x || a->y != b->y)
+			return 0;
+		if (a->u.wire.ex != b->u.wire.ex ||
+		    a->u.wire.ey != b->u.wire.ey)
+			return 0;
+		return 1;
+	case sch_obj_junction:
+		return 1;	
+	case sch_obj_noconn:
+		return 1;	
+	case sch_obj_text:
+		if (a->u.text.fn != b->u.text.fn)
+			return 0;
+		if (a->u.text.dir != b->u.text.dir)
+			return 0;
+		if (a->u.text.dim != b->u.text.dim)
+			return 0;
+		if (a->u.text.shape != b->u.text.shape)
+			return 0;
+		if (strcmp(a->u.text.s, b->u.text.s))
+			return 0;
+		return 1;
+	case sch_obj_comp:
+		if (a->u.comp.comp != b->u.comp.comp)
+			return 0;
+		if (a->u.comp.unit != b->u.comp.unit)
+			return 0;
+		if (memcmp(a->u.comp.m, b->u.comp.m, sizeof(a->u.comp.m)))
+			return 0;
+		return comp_fields_eq(a->u.comp.fields, b->u.comp.fields);
+	case sch_obj_sheet:
+		if (a->u.sheet.w != b->u.sheet.w)
+			return 0;
+		if (a->u.sheet.h != b->u.sheet.h)
+			return 0;
+		if (a->u.sheet.name_dim != b->u.sheet.name_dim)
+			return 0;
+		if (a->u.sheet.file_dim != b->u.sheet.file_dim)
+			return 0;
+		if (a->u.sheet.rotated != b->u.sheet.rotated)
+			return 0;
+		if (strcmp(a->u.sheet.name, b->u.sheet.name))
+			return 0;
+		if (strcmp(a->u.sheet.file, b->u.sheet.file))
+			return 0;
+		return sheet_fields_eq(a->u.sheet.fields, b->u.sheet.fields);
+	default:
+		abort();
+	}
+}
+
+
+static void free_obj(struct sch_obj *obj)
+{
+	/* there may be more to free once we get into cloning components */
+	free(obj);
+}
+
+
+static void init_res(struct sheet *res)
+{
+	res->title = NULL;
+        res->objs = NULL;
+        res->next_obj = &res->objs;
+        res->parent = NULL;
+        res->next = NULL;
+}
+
+
+void delta(const struct sheet *a, const struct sheet *b,
+    struct sheet *res_a, struct sheet *res_b, struct sheet *res_ab)
+{
+	struct sch_obj *objs_a, *objs_b;
+	struct sch_obj *next_a;
+	struct sch_obj **obj_b;
+
+	init_res(res_a);
+	init_res(res_b);
+	init_res(res_ab);
+
+	if (!strcmp(a->title, b->title)) {
+		res_ab->title = a->title;
+	} else {
+		res_a->title = a->title;
+		res_b->title = b->title;
+	}
+
+	objs_a = objs_clone(a->objs);
+	objs_b = objs_clone(b->objs);
+
+	while (objs_a) {
+		next_a = objs_a->next;
+		for (obj_b = &objs_b; *obj_b; obj_b = &(*obj_b)->next)
+			if (obj_eq(objs_a, *obj_b)) {
+				struct sch_obj *tmp = *obj_b;
+
+				add_obj(res_ab, objs_a);
+				*obj_b = tmp->next;
+				free_obj(tmp);
+				goto found;
+			}
+		add_obj(res_a, objs_a);
+found:
+		objs_a = next_a;
+	}
+	res_b->objs = objs_b;
+}
+
+
+void delta_free(struct sheet *d)
+{
+	struct sch_obj *next;
+
+	while (d->objs) {
+		next = d->objs->next;
+		free_obj(d->objs);
+		d->objs = next;
+	}
+}
diff --git a/eeshow/delta.h b/eeshow/delta.h
new file mode 100644
index 0000000..85dd5d5
--- /dev/null
+++ b/eeshow/delta.h
@@ -0,0 +1,24 @@
+/*
+ * delta.h - Find differences in .sch files
+ *
+ * Written 2016 by Werner Almesberger
+ * Copyright 2016 by Werner Almesberger
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+
+#ifndef DELTA_H
+#define DELTA_H
+
+#include "sch.h"
+
+
+void delta(const struct sheet *a, const struct sheet *b,
+    struct sheet *res_a, struct sheet *res_b, struct sheet *res_ab);
+void delta_free(struct sheet *d);
+
+#endif /* !DELTA_H */