diff --git a/crates/calc/src/eval.rs b/crates/calc/src/eval.rs
index 47a5119..0fbfdfb 100644
--- a/crates/calc/src/eval.rs
+++ b/crates/calc/src/eval.rs
@@ -407,6 +407,7 @@ impl<'h> Evaluator<'h> {
             };
         }
         let v = self.value(x);
+        let sys = self.host.workbook().date_system;
         Ev::V(map_unary(
             &v,
             &|n| match op {
@@ -416,6 +417,7 @@ impl<'h> Evaluator<'h> {
                 UnOp::At | UnOp::Spill | UnOp::Trim(_) => Value::number(n),
             },
             op == UnOp::Plus,
+            sys,
         ))
     }
 
@@ -502,7 +504,7 @@ impl<'h> Evaluator<'h> {
                 let mut acc = self.value(left);
                 while let Some((o, r)) = rest.pop() {
                     let y = self.value(r);
-                    acc = binary_values(o, &acc, &y);
+                    acc = binary_values(o, &acc, &y, self.host.workbook().date_system);
                 }
                 Ev::V(acc)
             }
@@ -1593,12 +1595,12 @@ impl Acc {
 
 // ---------------------------------------------------------------- operators
 
-fn map_unary(v: &Value, f: &dyn Fn(f64) -> Value, plus: bool) -> Value {
+fn map_unary(v: &Value, f: &dyn Fn(f64) -> Value, plus: bool, sys: gridcraft_core::DateSystem) -> Value {
     match v {
-        Value::Array(a) => Value::from(Array { rows: a.rows, cols: a.cols, data: a.data.iter().map(|x| map_unary(x, f, plus)).collect() }),
+        Value::Array(a) => Value::from(Array { rows: a.rows, cols: a.cols, data: a.data.iter().map(|x| map_unary(x, f, plus, sys)).collect() }),
         Value::Error(e) => Value::Error(*e),
         Value::Text(_) if plus => v.clone(),
-        other => match other.to_number() {
+        other => match other.to_number_in(sys) {
             Ok(n) => f(n),
             Err(e) => Value::Error(e),
         },
@@ -1651,18 +1653,18 @@ fn zip3(c: &Array, t: &Value, f: &Value, g: impl Fn(&Value, &Value, &Value) -> V
     Value::from(Array { rows, cols, data })
 }
 
-pub fn binary_values(op: BinOp, x: &Value, y: &Value) -> Value {
-    zip2(x, y, |a, b| binary_scalar(op, a, b))
+pub fn binary_values(op: BinOp, x: &Value, y: &Value, sys: gridcraft_core::DateSystem) -> Value {
+    zip2(x, y, |a, b| binary_scalar(op, a, b, sys))
 }
 
-fn binary_scalar(op: BinOp, a: &Value, b: &Value) -> Value {
+fn binary_scalar(op: BinOp, a: &Value, b: &Value, sys: gridcraft_core::DateSystem) -> Value {
     if let Value::Error(e) = a {
         return Value::Error(*e);
     }
     if let Value::Error(e) = b {
         return Value::Error(*e);
     }
-    let num = |f: fn(f64, f64) -> Value| match (a.to_number(), b.to_number()) {
+    let num = |f: fn(f64, f64) -> Value| match (a.to_number_in(sys), b.to_number_in(sys)) {
         (Ok(x), Ok(y)) => f(x, y),
         (Err(e), _) | (_, Err(e)) => Value::Error(e),
     };
diff --git a/crates/calc/src/tests.rs b/crates/calc/src/tests.rs
index a0c9fe2..1a26eb7 100644
--- a/crates/calc/src/tests.rs
+++ b/crates/calc/src/tests.rs
@@ -290,6 +290,26 @@ fn circular_references_without_iterative_calculation() {
     assert_eq!(t.get("A1"), Value::Error(CellError::Circ));
 }
 
+#[test]
+fn date_text_coerces_in_the_workbook_date_system() {
+    for (sys, serial) in [(gridcraft_core::DateSystem::D1900, 1462.0), (gridcraft_core::DateSystem::D1904, 0.0)] {
+        let mut t = T::new();
+        t.wb.date_system = sys;
+        t.set("A1", "'1/1/1904");
+        t.set("B1", "=A1+0");
+        t.set("C1", "=VALUE(A1)");
+        t.set("D1", "=-A1");
+        t.set("E1", "=DATEVALUE(A1)");
+        t.set("F1", "=NUMBERVALUE(A1)");
+        assert_eq!(t.get("A1"), Value::from("1/1/1904"));
+        assert_eq!(t.num("B1"), serial, "{sys:?}");
+        assert_eq!(t.num("C1"), serial, "{sys:?}");
+        assert_eq!(t.num("D1"), -serial, "{sys:?}");
+        assert_eq!(t.num("E1"), serial, "{sys:?}");
+        assert_eq!(t.num("F1"), serial, "{sys:?}");
+    }
+}
+
 #[test]
 fn operators() {
     let mut t = T::new();
diff --git a/crates/core/src/parse.rs b/crates/core/src/parse.rs
index a943103..b465bea 100644
--- a/crates/core/src/parse.rs
+++ b/crates/core/src/parse.rs
@@ -41,7 +41,12 @@ pub fn parse_input(s: &str, sys: DateSystem) -> Parsed {
 
 /// Numeric text as arithmetic coerces it ("1,000", "50%", "$3", "1/2/2020", "10:00").
 pub fn parse_number_text(s: &str) -> Option<f64> {
-    parse_numeric(s.trim(), DateSystem::D1900).map(|(n, _)| n)
+    parse_number_text_in(s, DateSystem::D1900)
+}
+
+/// Like [`parse_number_text`], with date text read in the given workbook date system.
+pub fn parse_number_text_in(s: &str, sys: DateSystem) -> Option<f64> {
+    parse_numeric(s.trim(), sys).map(|(n, _)| n)
 }
 
 fn parse_numeric(t: &str, sys: DateSystem) -> Option<(f64, Option<&'static str>)> {
diff --git a/crates/core/src/value.rs b/crates/core/src/value.rs
index 390800f..cfef7ac 100644
--- a/crates/core/src/value.rs
+++ b/crates/core/src/value.rs
@@ -224,13 +224,17 @@ impl Value {
     /// Coercion to a number as arithmetic does it: empty = 0, TRUE = 1, numeric text parses
     /// (including dates, times, percentages and currency), other text = `#VALUE!`.
     pub fn to_number(&self) -> Result<f64, CellError> {
+        self.to_number_in(crate::DateSystem::D1900)
+    }
+    /// [`Value::to_number`] with date text read in the given workbook date system.
+    pub fn to_number_in(&self, sys: crate::DateSystem) -> Result<f64, CellError> {
         match self {
             Value::Empty => Ok(0.0),
             Value::Number(n) => Ok(*n),
             Value::Bool(b) => Ok(if *b { 1.0 } else { 0.0 }),
-            Value::Text(t) => crate::parse::parse_number_text(t).ok_or(CellError::Value),
+            Value::Text(t) => crate::parse::parse_number_text_in(t, sys).ok_or(CellError::Value),
             Value::Error(e) => Err(*e),
-            Value::Array(a) => a.data.first().map(|v| v.to_number()).unwrap_or(Ok(0.0)),
+            Value::Array(a) => a.data.first().map(|v| v.to_number_in(sys)).unwrap_or(Ok(0.0)),
         }
     }
     /// Coercion to text as `&` does it.
diff --git a/crates/functions/src/text.rs b/crates/functions/src/text.rs
index 2b77196..ab7f1fc 100644
--- a/crates/functions/src/text.rs
+++ b/crates/functions/src/text.rs
@@ -1,6 +1,6 @@
 //! Text functions.
 
-use gridcraft_core::parse::parse_number_text;
+use gridcraft_core::parse::parse_number_text_in;
 use gridcraft_core::{CellError, Value, number_to_text};
 
 use crate::criteria::wildcard_find;
@@ -295,17 +295,17 @@ fn unicode(a: &[Arg], _c: &mut dyn Ctx) -> R<Value> {
 
 /// VALUE: a blank cell reads as 0, but empty or blank text is not a number (observed:
 /// `VALUE("")` is `#VALUE!`).
-fn value(a: &[Arg], _c: &mut dyn Ctx) -> R<Value> {
+fn value(a: &[Arg], c: &mut dyn Ctx) -> R<Value> {
     match scalar(arg(a, 0)?) {
         Value::Number(n) => num_val(n),
         Value::Empty => num_val(0.0),
         Value::Error(e) => Err(e),
-        Value::Text(t) => parse_number_text(&t).ok_or(CellError::Value).and_then(num_val),
+        Value::Text(t) => parse_number_text_in(&t, c.date_system()).ok_or(CellError::Value).and_then(num_val),
         _ => Err(CellError::Value),
     }
 }
 
-fn numbervalue(a: &[Arg], _c: &mut dyn Ctx) -> R<Value> {
+fn numbervalue(a: &[Arg], c: &mut dyn Ctx) -> R<Value> {
     let s = text(a, 0)?;
     let dec = if a.len() > 1 { text(a, 1)?.chars().next().ok_or(CellError::Value)? } else { '.' };
     let grp = if a.len() > 2 { text(a, 2)?.chars().next().ok_or(CellError::Value)? } else { ',' };
@@ -338,7 +338,7 @@ fn numbervalue(a: &[Arg], _c: &mut dyn Ctx) -> R<Value> {
             out.push(c);
         }
     }
-    let mut n = parse_number_text(&out).ok_or(CellError::Value)?;
+    let mut n = parse_number_text_in(&out, c.date_system()).ok_or(CellError::Value)?;
     for _ in 0..pct {
         n /= 100.0;
     }