diff --git a/src/main.rs b/src/main.rs
index 8f11f0e..e700625 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,6 +1,8 @@
 #![no_std]
 #![no_main]
 
+use core::ops::{Index, IndexMut};
+
 use arduino_hal::{
     adc::{
         channel::{ADC6, ADC7},
@@ -179,9 +181,11 @@ impl IOPins {
     }
 }
 
+#[derive(Clone, Copy, PartialEq, Eq)]
 enum SegmentState {
     Num(u8, bool),
     Minus,
+    Dot,
     Off,
 }
 
@@ -267,12 +271,13 @@ impl SegmentState {
                 }
             }
             SegmentState::Minus => seg.set_g(),
+            SegmentState::Dot => seg.set_dp(),
             SegmentState::Off => (),
         }
     }
 }
 
-struct DispalyState(pub [SegmentState; 9]);
+struct DispalyState([SegmentState; 9]);
 
 impl Default for DispalyState {
     fn default() -> DispalyState {
@@ -290,6 +295,40 @@ impl Default for DispalyState {
     }
 }
 
+impl Index<usize> for DispalyState {
+    type Output = SegmentState;
+
+    fn index(&self, index: usize) -> &Self::Output {
+        &self.0[index]
+    }
+}
+
+impl IndexMut<usize> for DispalyState {
+    fn index_mut(&mut self, index: usize) -> &mut Self::Output {
+        &mut self.0[index]
+    }
+}
+
+impl DispalyState {
+    fn set(&mut self, seg: [SegmentState; 9]) {
+        self.0 = seg;
+    }
+
+    fn busy(&mut self) {
+        self.set([
+            SegmentState::Off,
+            SegmentState::Dot,
+            SegmentState::Off,
+            SegmentState::Off,
+            SegmentState::Off,
+            SegmentState::Off,
+            SegmentState::Off,
+            SegmentState::Off,
+            SegmentState::Off,
+        ])
+    }
+}
+
 #[derive(uDebug, Clone, Copy, PartialEq, Eq)]
 enum InputKey {
     Up,
@@ -376,6 +415,88 @@ impl Debounce {
     }
 }
 
+#[derive(Default)]
+struct NumberInput {
+    minus: bool,
+    significant: [u8; 5],
+    minus_exponent: bool,
+    exponent: [u8; 2],
+    enter_exponent: bool,
+    significant_pos: usize,
+    exponent_pos: usize,
+}
+
+impl NumberInput {
+    fn reset(&mut self) {
+        *self = Self::default();
+    }
+    fn input_significant(&mut self, val: u8) -> Result<(), ()> {
+        if val > 9 {
+            panic!("Bad significatn val");
+        }
+        if self.significant_pos >= 5 {
+            return Err(());
+        }
+        self.significant[self.significant_pos] = val;
+        self.significant_pos += 1;
+        return Ok(());
+    }
+
+    fn input_exponent(&mut self, val: u8) -> Result<(), ()> {
+        if val > 9 {
+            panic!("Bad exponent val");
+        }
+        if self.exponent_pos >= 2 {
+            return Err(());
+        }
+        self.exponent[self.exponent_pos] = val;
+        self.exponent_pos += 1;
+        Ok(())
+    }
+
+    fn input(&mut self, val: u8) -> Result<(), ()> {
+        if self.enter_exponent {
+            self.input_exponent(val)
+        } else {
+            self.input_significant(val)
+        }
+    }
+
+    fn toggle_enter_exponent(&mut self) {
+        self.significant_pos = 0;
+        self.exponent_pos = 0;
+        self.enter_exponent = !self.enter_exponent;
+    }
+
+    fn toggle_minus(&mut self) {
+        if self.enter_exponent {
+            self.minus_exponent = !self.minus_exponent;
+        } else {
+            self.minus = !self.minus;
+        }
+    }
+
+    fn apply(&self, display: &mut DispalyState) {
+        display[0] = if self.minus {
+            SegmentState::Minus
+        } else {
+            SegmentState::Off
+        };
+        display[1] = SegmentState::Num(self.significant[0], true);
+        display[2] = SegmentState::Num(self.significant[1], false);
+        display[3] = SegmentState::Num(self.significant[2], false);
+        display[4] = SegmentState::Num(self.significant[3], false);
+        display[5] = SegmentState::Num(self.significant[4], false);
+        display[6] = if self.minus_exponent {
+            SegmentState::Minus
+        } else {
+            SegmentState::Off
+        };
+        display[7] = SegmentState::Num(self.exponent[0], false);
+        display[8] = SegmentState::Num(self.exponent[1], false);
+    }
+}
+
 #[arduino_hal::entry]
 fn main() -> ! {
     let dp = arduino_hal::Peripherals::take().unwrap();
@@ -415,17 +536,10 @@ fn main() -> ! {
     let mut adc = Adc::new(dp.ADC, Default::default());
     let input = Input::new(ADC7, ADC6);
     let mut debounce = Debounce::default();
+    let mut number_input = NumberInput::default();
 
     let mut display = DispalyState::default();
-    display.0[0] = SegmentState::Num(0, true);
-    display.0[1] = SegmentState::Num(1, false);
-    display.0[2] = SegmentState::Num(2, false);
-    display.0[3] = SegmentState::Num(3, false);
-    display.0[4] = SegmentState::Num(4, false);
-    display.0[5] = SegmentState::Num(5, false);
-    display.0[6] = SegmentState::Num(6, false);
-    display.0[7] = SegmentState::Num(7, false);
-    display.0[8] = SegmentState::Num(8, false);
+    number_input.apply(&mut display);
 
     loop {
         let mut key: Option<(usize, bool, bool)> = None;
@@ -444,9 +558,25 @@ fn main() -> ! {
         }
 
         let key = key.and_then(|(no, kn, ko)| InputKey::map(no, kn, ko));
+        // TODO: impl main state
+        let mut err = Ok(());
 
         if let Some(key) = debounce.input(key) {
             ufmt::uwriteln!(&mut serial, "key: {:?}", key).unwrap_infallible();
+            match key {
+                InputKey::Up => todo!(),
+                InputKey::C => number_input.reset(),
+                InputKey::Num(val) => {
+                    err = number_input.input(val);
+                }
+                InputKey::Mul => todo!(),
+                InputKey::Div => todo!(),
+                InputKey::Plus => todo!(),
+                InputKey::Minus => number_input.toggle_minus(),
+                InputKey::Down => todo!(),
+                InputKey::E => number_input.toggle_enter_exponent(),
+            }
+            number_input.apply(&mut display);
         }
         arduino_hal::delay_ms(1);
     }