diff --git a/DSView/pv/data/dsosnapshot.cpp b/DSView/pv/data/dsosnapshot.cpp
index 11f5d8aa..fa0957b0 100644
--- a/DSView/pv/data/dsosnapshot.cpp
+++ b/DSView/pv/data/dsosnapshot.cpp
@@ -265,7 +265,7 @@ void DsoSnapshot::enable_envelope(bool enable)
     _envelope_en = enable;
 }
 
-const uint8_t *DsoSnapshot::get_samples(int64_t start_sample, int64_t end_sample, uint16_t index)
+const uint8_t *DsoSnapshot::get_samples(int64_t start_sample, int64_t end_sample, uint16_t ch_index)
 {
     std::lock_guard<std::mutex> lock(_mutex);
 
@@ -275,10 +275,10 @@ const uint8_t *DsoSnapshot::get_samples(int64_t start_sample, int64_t end_sample
     assert(end_sample < (int64_t)_sample_count);
 	assert(start_sample <= end_sample);
 
-    int order = get_ch_order(index);
+    int order = get_ch_order(ch_index);
 
     if (order == -1){
-        dsv_err("The channel index is not exist:%d", index);
+        dsv_err("The channel index is not exist:%d", ch_index);
         assert(false);
     } 
 
diff --git a/DSView/pv/data/dsosnapshot.h b/DSView/pv/data/dsosnapshot.h
index 119b812f..0d9725e0 100644
--- a/DSView/pv/data/dsosnapshot.h
+++ b/DSView/pv/data/dsosnapshot.h
@@ -89,7 +89,7 @@ public:
                        GSList *channels, bool instant, bool isFile);
 
     void append_payload(const sr_datafeed_dso &dso);
-    const uint8_t* get_samples(int64_t start_sample, int64_t end_sample, uint16_t index);
+    const uint8_t* get_samples(int64_t start_sample, int64_t end_sample, uint16_t ch_index);
 
 	void get_envelope_section(EnvelopeSection &s,
         uint64_t start, uint64_t end, float min_length, int probe_index);
diff --git a/DSView/pv/data/mathstack.cpp b/DSView/pv/data/mathstack.cpp
index a3656af6..01474aea 100644
--- a/DSView/pv/data/mathstack.cpp
+++ b/DSView/pv/data/mathstack.cpp
@@ -325,6 +325,9 @@ void MathStack::calc_math()
     if (!_dsoSig1->enabled() || !_dsoSig2->enabled())
         return;
 
+    if (data->get_channel_num() < 2)
+        return;
+
     const double scale1 = _dsoSig1->get_vDialValue() / 1000.0 * _dsoSig1->get_factor() * DS_CONF_DSO_VDIVS *
                           _dsoSig1->get_scale() / _dsoSig1->get_view_rect().height();
     const double delta1 = _dsoSig1->get_hw_offset() * scale1;
@@ -333,18 +336,19 @@ void MathStack::calc_math()
                           _dsoSig2->get_scale() / _dsoSig2->get_view_rect().height();
     const double delta2 = _dsoSig2->get_hw_offset() * scale2;
 
-    const int index1 = _dsoSig1->get_index();
-    const int index2 = _dsoSig2->get_index();
-
-    const int num_channels = data->get_channel_num();
-    const uint8_t* value = data->get_samples(0, 0, 0);
     _sample_num = data->get_sample_count();
     assert(_sample_num <= _total_sample_num);
 
+    const int index1 = _dsoSig1->get_index();
+    const int index2 = _dsoSig2->get_index();
+    const uint8_t* value_buffer1 = data->get_samples(0, 0, index1);
+    const uint8_t* value_buffer2 = data->get_samples(0, 0, index2);
     double value1, value2;
+
     for (uint64_t sample = 0; sample < _sample_num; sample++) {
-        value1 = value[sample * num_channels + index1];
-        value2 = value[sample * num_channels + index2];
+        value1 = *(value_buffer1 + sample);
+        value2 = *(value_buffer2 + sample);
+
         switch(_type) {
         case MATH_ADD:
             _math[sample] = (delta1 - scale1 * value1) + (delta2 - scale2 * value2);