diff --git a/Makefile b/Makefile
index 972ecd6..67e05d6 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,7 @@
 CFLAGS=		-g -Wall -O2 -Wc++-compat
 CPPFLAGS=	-DHAVE_KALLOC
 INCLUDES=
-OBJS=		kthread.o kalloc.o misc.o bseq.o sketch.o sdust.o index.o chain.o align.o hit.o map.o format.o pe.o ksw2_ll_sse.o
+OBJS=		kthread.o kalloc.o misc.o bseq.o sketch.o sdust.o index.o chain.o align.o hit.o map.o format.o pe.o esterr.o ksw2_ll_sse.o
 PROG=		minimap2
 PROG_EXTRA=	sdust minimap2-lite
 LIBS=		-lm -lz -lpthread
diff --git a/format.c b/format.c
index efb0d3e..fb8924d 100644
--- a/format.c
+++ b/format.c
@@ -210,6 +210,12 @@ static inline void write_tags(kstring_t *s, const mm_reg1_t *r)
 	}
 	mm_sprintf_lite(s, "\ttp:A:%c\tcm:i:%d\ts1:i:%d", type, r->cnt, r->score);
 	if (r->parent == r->id) mm_sprintf_lite(s, "\ts2:i:%d", r->subsc);
+	if (r->div >= 0.0f && r->div <= 1.0f) {
+		char buf[8];
+		if (r->div == 0.0f) buf[0] = '0', buf[1] = 0;
+		else sprintf(buf, "%.4f", r->div);
+		mm_sprintf_lite(s, "\tdv:f:%s", buf);
+	}
 	if (r->split) mm_sprintf_lite(s, "\tzd:i:%d", r->split);
 }
 
diff --git a/main.c b/main.c
index c91dc4d..3b71b74 100644
--- a/main.c
+++ b/main.c
@@ -6,7 +6,7 @@
 #include "mmpriv.h"
 #include "getopt.h"
 
-#define MM_VERSION "2.5-r606-dirty"
+#define MM_VERSION "2.5-r607-dirty"
 
 #ifdef __linux__
 #include <sys/resource.h>
diff --git a/map.c b/map.c
index 6330f88..b9177ae 100644
--- a/map.c
+++ b/map.c
@@ -125,6 +125,8 @@ struct mm_tbuf_s {
 	sdust_buf_t *sdb;
 	mm128_v mini;
 	void *km;
+	int32_t n_mini_pos;
+	uint64_t *mini_pos;
 };
 
 mm_tbuf_t *mm_tbuf_init(void)
@@ -139,6 +141,7 @@ mm_tbuf_t *mm_tbuf_init(void)
 void mm_tbuf_destroy(mm_tbuf_t *b)
 {
 	if (b == 0) return;
+	kfree(b->km, b->mini_pos);
 	kfree(b->km, b->mini.a);
 	sdust_buf_destroy(b->sdb);
 	km_destroy(b->km);
@@ -188,6 +191,8 @@ static mm128_t *collect_seed_hits(const mm_mapopt_t *opt, int max_occ, const mm_
 	mm_match_t *m;
 	mm128_t *a;
 
+	b->n_mini_pos = 0;
+	b->mini_pos = (uint64_t*)kmalloc(b->km, b->mini.n * sizeof(uint64_t));
 	m = (mm_match_t*)kmalloc(b->km, b->mini.n * sizeof(mm_match_t));
 	for (i = 0; i < b->mini.n; ++i) {
 		int t;
@@ -213,6 +218,7 @@ static mm128_t *collect_seed_hits(const mm_mapopt_t *opt, int max_occ, const mm_
 			} else rep_en = en;
 			continue;
 		}
+		b->mini_pos[b->n_mini_pos++] = (uint64_t)q_span<<32 | q->qpos>>1;
 		if (i > 0 && p->x>>8 == b->mini.a[i - 1].x>>8) is_tandem = 1;
 		if (i < b->mini.n - 1 && p->x>>8 == b->mini.a[i + 1].x>>8) is_tandem = 1;
 		for (k = 0; k < q->n; ++k) {
@@ -342,6 +348,7 @@ void mm_map_frag(const mm_idx_t *mi, int n_segs, const int *qlens, const char **
 						i == regs0[j].as? 0 : ((int32_t)a[i].y - (int32_t)a[i-1].y) - ((int32_t)a[i].x - (int32_t)a[i-1].x));
 
 	chain_post(opt, max_chain_gap_ref, mi, b->km, qlen_sum, n_segs, qlens, &n_regs0, regs0, a);
+	if (!is_sr) mm_est_err(qlen_sum, n_regs0, regs0, a, b->n_mini_pos, b->mini_pos);
 
 	if (n_segs == 1) { // uni-segment
 		regs0 = align_regs(opt, mi, b->km, qlens[0], seqs[0], quals? quals[0] : 0, &n_regs0, regs0, a);
diff --git a/minimap.h b/minimap.h
index 45a8f30..b33ffb3 100644
--- a/minimap.h
+++ b/minimap.h
@@ -68,17 +68,19 @@ typedef struct {
 } mm_extra_t;
 
 typedef struct {
-	int32_t id;                     // ID for internal uses (see also parent below)
-	uint32_t cnt:28, rev:1, seg_split:1, sam_pri:1, proper_frag:1; // number of minimizers; if on the reverse strand
-	uint32_t rid:31, inv:1;         // reference index; if this is an alignment from inversion rescue
-	int32_t score;                  // DP alignment score
-	int32_t qs, qe, rs, re;         // query start and end; reference start and end
-	int32_t parent, subsc;          // parent==id if primary; best alternate mapping score
-	int32_t as;                     // offset in the a[] array (for internal uses only)
-	int32_t mlen, blen;             // seeded exact match length; seeded alignment block length
-	uint32_t mapq:8, split:2, n_sub:22; // mapQ; split pattern; number of suboptimal mappings
-	uint32_t pe_thru:1, score0:31;
+	int32_t id;             // ID for internal uses (see also parent below)
+	int32_t cnt;            // number of minimizers; if on the reverse strand
+	int32_t rid;            // reference index; if this is an alignment from inversion rescue
+	int32_t score;          // DP alignment score
+	int32_t qs, qe, rs, re; // query start and end; reference start and end
+	int32_t parent, subsc;  // parent==id if primary; best alternate mapping score
+	int32_t as;             // offset in the a[] array (for internal uses only)
+	int32_t mlen, blen;     // seeded exact match length; seeded alignment block length
+	int32_t n_sub;          // number of suboptimal mappings
+	int32_t score0;         // initial chaining score (before chain merging/spliting)
+	uint32_t mapq:8, split:2, rev:1, inv:1, sam_pri:1, proper_frag:1, pe_thru:1, seg_split:1, dummy:16;
 	uint32_t hash;
+	float div;
 	mm_extra_t *p;
 } mm_reg1_t;
 
diff --git a/mmpriv.h b/mmpriv.h
index e0b06c9..9ec080e 100644
--- a/mmpriv.h
+++ b/mmpriv.h
@@ -79,6 +79,8 @@ void mm_join_long(void *km, const mm_mapopt_t *opt, int qlen, int *n_regs, mm_re
 void mm_hit_sort_by_dp(void *km, int *n_regs, mm_reg1_t *r);
 void mm_set_mapq(int n_regs, mm_reg1_t *regs, int min_chain_sc, int match_sc, int rep_len, int is_sr);
 
+void mm_est_err(int qlen, int n_regs, mm_reg1_t *regs, const mm128_t *a, int32_t n, uint64_t *mini_pos);
+
 mm_seg_t *mm_seg_gen(void *km, uint32_t hash, int n_segs, const int *qlens, int n_regs0, const mm_reg1_t *regs0, int *n_regs, mm_reg1_t **regs, const mm128_t *a);
 void mm_seg_free(void *km, int n_segs, mm_seg_t *segs);
 void mm_pair(void *km, int max_gap_ref, int dp_bonus, int sub_diff, int match_sc, const int *qlens, int *n_regs, mm_reg1_t **regs);