diff --git a/cli/config.cpp b/cli/config.cpp
index cc24475..b03b3c8 100644
--- a/cli/config.cpp
+++ b/cli/config.cpp
@@ -22,7 +22,9 @@ Config::Config(int argc, char *argv[])
 	bool show_help{}, show_version{};
 	auto cli_head = (
 		clipp::option("-h", "--help").set(show_help).doc("This help"),
-		clipp::option("-V", "--version").set(show_version).doc("Version"),
+		clipp::option("-V", "--version").set(show_version).doc("Version")
+	);
+	auto cli_mod = "Run modifiers:" % (
 		clipp::option("-v", "--verbose").call([]{
 			spdlog::set_level(spdlog::level::debug);
 		}).doc("Enable verbose output"),
@@ -35,9 +37,9 @@ Config::Config(int argc, char *argv[])
 			.doc("Display interval in seconds")
 	);
 
-	auto cli_output = "Output:" % (
-		clipp::option("-A", "--ascii").set(m_output_type,ASCII).doc("ASCII output") |
-		clipp::option("-U", "--unicode").set(m_output_type,UNICODE).doc("Unicode output") |
+	auto cli_output = "Output:" % one_of (
+		clipp::option("-A", "--ascii").set(m_output_type,ASCII).doc("ASCII output"),
+		clipp::option("-U", "--unicode").set(m_output_type,UNICODE).doc("Unicode output"),
 		clipp::option("-B", "--braille").set(m_output_type,BRAILLE).doc("Braille output")
 	);
 
@@ -53,6 +55,7 @@ Config::Config(int argc, char *argv[])
 
 	auto cli = (
 		cli_head | (
+			cli_mod,
 			cli_output,
 			clipp::repeatable(
 				/* select a plot type */
@@ -98,8 +101,10 @@ Config::Config(int argc, char *argv[])
 						.doc("Find numbers in input line, pick 1 or 2 positions for X and Y values"),
 					(clipp::option("-r", "--regex") & clipp::value("regex")
 						.call([&](const char *txt) { m_inputs.back().set_regex(txt); }))
-						.doc("Regex to match numbers from input line")
-
+						.doc("Regex to match numbers from input line"),
+					(clipp::option("-l", "--limit") & clipp::value("count")
+						.call([&](const char *txt) { m_inputs.back().set_data_limit(txt); }))
+						.doc("How many historical values to retain for plotting")
 				),
 
 				"Plot modifiers:" % (
@@ -169,6 +174,7 @@ Config::Config(int argc, char *argv[])
 
 	bool with_interval{}, no_interval{};
 	double prev_interval = 1;
+	size_t prev_data_limit = Input::g_default_data_limit;
 	for (auto &input : m_inputs) {
 		if (input.needs_interval()) {
 			if (!input.interval()) {
@@ -177,6 +183,11 @@ Config::Config(int argc, char *argv[])
 				prev_interval = input.interval();
 			}
 		}
+		if (!input.data_limit()) {
+			input.set_data_limit(prev_data_limit);
+		} else {
+			prev_data_limit = input.data_limit();
+		}
 		if (!input) {
 			spdlog::error("incomplete plot definition");
 			std::exit(1);
@@ -316,6 +327,19 @@ void Input::set_interval (const std::string &txt)
 		std::exit(1);
 	}
 }
+void Input::set_data_limit (size_t value)
+{
+	m_data_limit = value;
+}
+void Input::set_data_limit (const std::string &txt)
+{
+	auto [_,ec] = std::from_chars(txt.data(), txt.data()+txt.size(), m_data_limit);
+	if (ec != std::errc{}) {
+		spdlog::error("failed to parse data limit from '{}': {}",
+			txt, std::make_error_code(ec).message());
+		std::exit(1);
+	}
+}
 
 Input::operator bool() const
 {
diff --git a/cli/config.hpp b/cli/config.hpp
index eb24c18..b43c227 100644
--- a/cli/config.hpp
+++ b/cli/config.hpp
@@ -20,6 +20,8 @@ class  Input final {
 		WATCH		// run program repetitively at interval, each run is one entry
 	};
 
+	static constexpr const size_t g_default_data_limit = 1000000;
+
 protected:
 	blot_plot_type m_plot_type{BLOT_LINE};
 	Source m_source{NONE};
@@ -27,6 +29,7 @@ class  Input final {
 	Extract m_extract;
 	blot_color m_plot_color;
 	double m_interval{0};
+	size_t m_data_limit{g_default_data_limit};
 
 public:
 	explicit Input(blot_plot_type plot_type, blot_color color)
@@ -63,6 +66,7 @@ class  Input final {
 	const Extract& extract() const { return m_extract; }
 	blot_color plot_color() const { return m_plot_color; }
 	double interval() const { return m_interval; }
+	size_t data_limit() const { return m_data_limit; }
 
 	/* validate if the configuration looks sane */
 	operator bool() const;
@@ -73,14 +77,19 @@ class  Input final {
 	void set_color (const std::string &txt);
 	void set_interval (double interval);
 	void set_interval (const std::string &txt);
+	void set_data_limit (size_t);
+	void set_data_limit (const std::string &txt);
 
 
 };
 
 class  Config final {
+public:
+	using OutputType = enum output_type { ASCII, UNICODE, BRAILLE };
+
 protected:
 	const char *m_self{};
-	enum output_type { ASCII, UNICODE, BRAILLE } m_output_type;
+	OutputType  m_output_type;
 	const static blot_color m_first_color{9};
 	std::vector<Input> m_inputs;
 	bool m_display_interval{1};
@@ -100,8 +109,9 @@ class  Config final {
 		}
 	}
 
-	size_t inputs() const { return m_inputs.size(); }
+	OutputType output_type() const { return m_output_type; }
 
+	size_t inputs() const { return m_inputs.size(); }
 	const Input& input(size_t n) const { return m_inputs.at(n); }
 	Input& input(size_t n) { return m_inputs.at(n); }
 
diff --git a/cli/plotter.hpp b/cli/plotter.hpp
index 08ed3f2..a51d39a 100644
--- a/cli/plotter.hpp
+++ b/cli/plotter.hpp
@@ -9,9 +9,49 @@
 template <typename X, typename Y>
 class Plotter final {
 protected:
+	template <typename T>
+	class Storage {
+	protected:
+		std::vector<T> m_data;
+		size_t m_offset{};
+
+		void relocation_check() {
+			bool full = m_data.size() == m_data.capacity();
+			if (full && m_offset && m_offset > (m_data.capacity()/2)) {
+				// full but most is empty, so we should relocate the data
+				m_data.erase(m_data.begin(), m_data.begin() + m_offset);
+				m_offset = 0;
+			}
+		}
+
+	public:
+		void push_back(const T &v) {
+			relocation_check();
+			m_data.push_back(v);
+		}
+
+		void erase_front(size_t count = 1) {
+			if (count > size())
+				BLOT_THROW(ERANGE, "count=%zu exceeds size=%zu", count, size());
+			m_offset += count;
+		}
+
+		T* data() noexcept { return m_data.data() + m_offset; }
+		const T* data() const noexcept { return m_data.data() + m_offset; }
+		size_t size() const { return m_data.size() - m_offset; }
+
+		std::span<T> span() {
+			return std::span<const T>(data(), size());
+		}
+		std::span<const T> span() const {
+			return std::span<const T>(data(), size());
+		}
+
+	};
+
 	struct Data {
-		std::vector<X> m_xs;
-		std::vector<Y> m_ys;
+		Storage<X> m_xs;
+		Storage<Y> m_ys;
 	};
 	std::vector<Data> m_data;
 	size_t m_count{};
@@ -41,6 +81,11 @@ class Plotter final {
 		m_data[layer].m_xs.push_back(x);
 		m_data[layer].m_ys.push_back(y);
 		m_count ++;
+
+		if (m_data[layer].m_xs.size() > m_config.input(layer).data_limit()) {
+			m_data[layer].m_xs.erase_front();
+			m_data[layer].m_ys.erase_front();
+		}
 	}
 
 	bool have_data() const { return m_count > 0; }
@@ -67,17 +112,27 @@ class Plotter final {
 			const auto &data = m_data[i];
 			const auto &input = m_config.input(i);
 
-			fig.plot(input.plot_type(), data.m_xs, data.m_ys,
+			fig.plot(input.plot_type(), data.m_xs.span(), data.m_ys.span(),
 				input.plot_color(), input.details());
 		}
 
 		double t_add = timing ? blot_double_time() : 0;
 
 		blot_render_flags flags
-			= BLOT_RENDER_BRAILLE
-			| BLOT_RENDER_LEGEND_BELOW
+			= BLOT_RENDER_LEGEND_BELOW
 			| BLOT_RENDER_CLEAR;
 
+		switch (m_config.output_type()) {
+			case Config::ASCII:
+				flags = flags | BLOT_RENDER_NO_UNICODE;
+				break;
+			case Config::BRAILLE:
+				flags = flags | BLOT_RENDER_BRAILLE;
+				break;
+			default: // UNICODE
+				break;
+		}
+
 		if (timing)
 			flags = flags | BLOT_RENDER_LEGEND_DETAILS;
 
diff --git a/include/blot.hpp b/include/blot.hpp
index 7215c66..5f502b3 100644
--- a/include/blot.hpp
+++ b/include/blot.hpp
@@ -5,6 +5,7 @@
 
 #include <cassert>
 #include <iostream>
+#include <span>
 #include <stdexcept>
 #include <algorithm>
 #include <utility>
@@ -86,15 +87,15 @@ class Exception final : public std::exception {
 
 template <typename T>
 constexpr blot_data_type data_type() {
-	if constexpr (std::is_same_v<T, int16_t>)
+	if constexpr (std::is_same_v<std::remove_const_t<T>, int16_t>)
 		return BLOT_DATA_INT16;
-	else if constexpr (std::is_same_v<T, int32_t>)
+	else if constexpr (std::is_same_v<std::remove_const_t<T>, int32_t>)
 		return BLOT_DATA_INT32;
-	else if constexpr (std::is_same_v<T, int64_t>)
+	else if constexpr (std::is_same_v<std::remove_const_t<T>, int64_t>)
 		return BLOT_DATA_INT64;
-	else if constexpr (std::is_same_v<T, float>)
+	else if constexpr (std::is_same_v<std::remove_const_t<T>, float>)
 		return BLOT_DATA_FLOAT;
-	else if constexpr (std::is_same_v<T, double>)
+	else if constexpr (std::is_same_v<std::remove_const_t<T>, double>)
 		return BLOT_DATA_DOUBLE;
 	else
 		BLOT_THROW(EINVAL, "unsupported type");
@@ -184,7 +185,7 @@ struct Figure final : public blot_figure {
 	/* add layers */
 
 	template <typename T, typename U>
-	void plot(blot_plot_type plot_type, const std::vector<T> &data_xs, const std::vector<U> &data_ys, blot_color data_color, const char *data_label) {
+	void plot(blot_plot_type plot_type, const std::span<T> &data_xs, const std::span<U> &data_ys, blot_color data_color, const char *data_label) {
 		GError *error = nullptr;
 		size_t data_count = data_ys.size();
 
@@ -206,6 +207,14 @@ struct Figure final : public blot_figure {
 		}
 	}
 
+	template <typename T, typename U>
+	void plot(blot_plot_type plot_type, const std::vector<T> &data_xs, const std::vector<U> &data_ys, blot_color data_color, const char *data_label) {
+		plot(plot_type,
+		       std::span<const T>(data_xs.data(), data_xs.size()),
+		       std::span<const U>(data_ys.data(), data_ys.size()),
+		       data_color, data_label);
+	}
+
 	template <typename T, typename U>
 	void scatter(const std::vector<T> &data_xs, const std::vector<U>& data_ys, blot_color data_color, const char *data_label) {
 		plot(BLOT_SCATTER, data_xs, data_ys, data_color, data_label);