diff --git a/src/calc.rs b/src/calc.rs
index f9339d5..e951b8f 100644
--- a/src/calc.rs
+++ b/src/calc.rs
@@ -333,7 +333,7 @@ impl<'a> Calculator<'a> {
             push: OpArgs::Unary(f),
         })
     }
-    fn pop(&mut self) -> CalculatorResult<f64> {
+    pub fn pop(&mut self) -> CalculatorResult<f64> {
         let f = self.checked_get(0)?;
         self.direct_state_change(CalculatorStateChange {
             pop: OpArgs::Unary(f),
@@ -341,6 +341,15 @@ impl<'a> Calculator<'a> {
         })?;
         Ok(f)
     }
+    pub fn pop_usize(&mut self) -> CalculatorResult<usize> {
+        let f = self.checked_get(0)?;
+        let ret = usize::from(f as usize);
+        self.direct_state_change(CalculatorStateChange {
+            pop: OpArgs::Unary(f),
+            push: OpArgs::None,
+        })?;
+        Ok(ret)
+    }
     pub fn op(&mut self, op: CalculatorOperation) -> CalculatorResult<()> {
         // Dup is special -- don't actually run it if l needs to be flushed
         if self.flush_l()? {
diff --git a/src/main.rs b/src/main.rs
index 01143ec..60fef14 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -27,7 +27,18 @@ struct Dimensions {
     height: u16,
 }
 
+enum DisplayMode {
+    Default(Option<char>),
+    Scientific(usize),
+    Engineering,
+}
+
+struct AppSettings {
+    display_mode: DisplayMode,
+}
+
 enum AppState {
+    AppSettings,
     Calculator,
     Help,
 }
@@ -37,6 +48,7 @@ struct App<'a> {
     error_msg: Option<String>,
     state: AppState,
     current_macro: Option<char>,
+    app_settings: AppSettings,
 }
 
 impl<'a> Default for App<'a> {
@@ -46,6 +58,9 @@ impl<'a> Default for App<'a> {
             error_msg: None,
             state: AppState::Calculator,
             current_macro: None,
+            app_settings: AppSettings {
+                display_mode: DisplayMode::Default(None),
+            },
         }
     }
 }
@@ -80,13 +95,24 @@ fn main() -> Result<(), Box<dyn Error>> {
                     Span::raw("Error: "),
                     Span::styled(e, Style::default().add_modifier(Modifier::RAPID_BLINK)),
                 ],
-                (None, AppState::Calculator) => vec![
-                    Span::raw("Press "),
-                    Span::styled("q", Style::default().add_modifier(Modifier::BOLD)),
-                    Span::raw(" to exit, "),
-                    Span::styled("h", Style::default().add_modifier(Modifier::BOLD)),
-                    Span::raw(" for help"),
-                ],
+                (None, AppState::Calculator) => {
+                    // TODO: There has to be a better way than making strings each time
+                    let display_mode_str = match &app.app_settings.display_mode {
+                        DisplayMode::Default(None) => String::from("[d]"),
+                        DisplayMode::Default(Some(c)) => format!("[d({})]", c),
+                        DisplayMode::Scientific(p) => format!("[s({})]", p),
+                        DisplayMode::Engineering => String::from("[e]"),
+                    };
+
+                    vec![
+                        Span::raw("Press "),
+                        Span::styled("q", Style::default().add_modifier(Modifier::BOLD)),
+                        Span::raw(" to exit, "),
+                        Span::styled("h", Style::default().add_modifier(Modifier::BOLD)),
+                        Span::raw(" for help - "),
+                        Span::raw(display_mode_str),
+                    ]
+                }
                 (None, _) => vec![
                     Span::raw("Press "),
                     Span::styled("<esc>", Style::default().add_modifier(Modifier::BOLD)),
@@ -106,7 +132,16 @@ fn main() -> Result<(), Box<dyn Error>> {
                 .enumerate()
                 .rev()
                 .map(|(i, m)| {
-                    let content = vec![Spans::from(Span::raw(format!("{}: {}", i, m)))];
+                    let content = vec![Spans::from(Span::raw(
+                        match &app.app_settings.display_mode {
+                            DisplayMode::Default(None) => format!("{:>2}: {}", i, *m),
+                            DisplayMode::Default(Some(c)) => fmt_separated(i, *m, *c),
+                            DisplayMode::Scientific(precision) => fmt_scientific(i, *m, *precision),
+                            DisplayMode::Engineering => {
+                                format!("{:>2}: {}", i, m)
+                            }
+                        },
+                    ))];
                     ListItem::new(content)
                 })
                 .collect();
@@ -134,6 +169,22 @@ fn main() -> Result<(), Box<dyn Error>> {
             );
 
             match (&app.state, app.calculator.get_state()) {
+                (AppState::AppSettings, _) => {
+                    draw_clippy_rect(
+                        ClippyRectangle {
+                            title: "App Settings",
+                            msg: "\
+                            d   => Default\n\
+                            ,   => Default (comma separated)\n\
+                            s   => Scientific\n\
+                            S   => Scientific (stack precision)\n\
+                            e   => Engineering\n\
+                            E   => Engineering (stack precision)\n\
+                            ",
+                        },
+                        f,
+                    );
+                }
                 (AppState::Help, _) => {
                     draw_clippy_rect(
                         ClippyRectangle {
@@ -248,6 +299,9 @@ fn handle_key(app: &mut App, events: &Events, key: Key) -> CalculatorResult<bool
             Key::Char('h') => {
                 app.state = AppState::Help;
             }
+            Key::Ctrl('s') => {
+                app.state = AppState::AppSettings;
+            }
             Key::Char('\n') | Key::Char(' ') => {
                 app.calculator.take_input(' ')?;
             }
@@ -265,6 +319,20 @@ fn handle_key(app: &mut App, events: &Events, key: Key) -> CalculatorResult<bool
             }
             _ => {}
         },
+        (AppState::AppSettings, _) => match key {
+            Key::Esc | Key::Char('q') => {
+                app.state = AppState::Calculator;
+                app.calculator.cancel()?;
+            }
+            Key::Char('d') => app.app_settings.display_mode = DisplayMode::Default(None),
+            Key::Char(',') => app.app_settings.display_mode = DisplayMode::Default(Some(',')),
+            Key::Char('s') => app.app_settings.display_mode = DisplayMode::Scientific(3),
+            Key::Char('S') => {
+                app.app_settings.display_mode = DisplayMode::Scientific(app.calculator.pop_usize()?)
+            }
+            Key::Char('e') => app.app_settings.display_mode = DisplayMode::Engineering,
+            _ => {}
+        },
         (AppState::Help, _) => match key {
             Key::Esc | Key::Char('q') => {
                 app.state = AppState::Calculator;
@@ -336,3 +404,33 @@ fn draw_clippy_rect<T: std::io::Write>(c: ClippyRectangle, f: &mut Frame<Termion
         .block(Block::default().borders(Borders::ALL).title(c.title));
     f.render_widget(help_message, area);
 }
+
+fn fmt_scientific(i: usize, f: f64, precision: usize) -> String {
+    let mut ret = format!("{:.precision$e}", f, precision = precision);
+    let exp = ret.split_off(ret.find('e').unwrap_or(0));
+    let (pow_sign, exp) = if exp.starts_with("e-") {
+        ('-', &exp[2..])
+    } else {
+        ('+', &exp[1..])
+    };
+    let sign = if !ret.starts_with('-') { " " } else { "" };
+    format!(
+        "{:>2}: {}{}e{}{:0>pad$}",
+        i,
+        sign,
+        ret,
+        pow_sign,
+        exp,
+        pad = 2
+    )
+}
+
+fn fmt_separated(i: usize, f: f64, sep: char) -> String {
+    let mut ret = f.to_string();
+    let start = if ret.starts_with('-') { 1 } else { 0 };
+    let end = ret.find('.').unwrap_or(ret.len());
+    for i in 0..((end - start).div_euclid(3)) {
+        ret.insert(end - start - (i + 1) * 3, sep);
+    }
+    format!("{:>2}: {}", i, ret)
+}