diff --git a/base/src/cast.rs b/base/src/cast.rs
index 912594d..33fe7af 100644
--- a/base/src/cast.rs
+++ b/base/src/cast.rs
@@ -15,6 +15,23 @@ pub(crate) enum NumberOrArray {
 }
 
 impl Model {
+    pub(crate) fn cast_number(&self, s: &str) -> Option<f64> {
+        match s.trim().parse::<f64>() {
+            Ok(f) => Some(f),
+            _ => {
+                let currency = &self.locale.currency.symbol;
+                let mut currencies = vec!["$", "€"];
+                if !currencies.iter().any(|e| *e == currency) {
+                    currencies.push(currency);
+                }
+                // Try to parse as a formatted number (e.g., dates, currencies, percentages)
+                if let Ok((v, _number_format)) = parse_formatted_number(s, &currencies) {
+                    return Some(v);
+                }
+                None
+            }
+        }
+    }
     pub(crate) fn get_number_or_array(
         &mut self,
         node: &Node,
@@ -22,24 +39,13 @@ impl Model {
     ) -> Result<NumberOrArray, CalcResult> {
         match self.evaluate_node_in_context(node, cell) {
             CalcResult::Number(f) => Ok(NumberOrArray::Number(f)),
-            CalcResult::String(s) => match s.parse::<f64>() {
-                Ok(f) => Ok(NumberOrArray::Number(f)),
-                _ => {
-                    let mut currencies = vec!["$", "€"];
-                    let currency = &self.locale.currency.symbol;
-                    if !currencies.iter().any(|e| e == currency) {
-                        currencies.push(currency);
-                    }
-                    // Try to parse as a formatted number (e.g., dates, currencies, percentages)
-                    if let Ok((v, _number_format)) = parse_formatted_number(&s, &currencies) {
-                        return Ok(NumberOrArray::Number(v));
-                    }
-                    Err(CalcResult::new_error(
-                        Error::VALUE,
-                        cell,
-                        "Expecting number".to_string(),
-                    ))
-                }
+            CalcResult::String(s) => match self.cast_number(&s) {
+                Some(f) => Ok(NumberOrArray::Number(f)),
+                None => Err(CalcResult::new_error(
+                    Error::VALUE,
+                    cell,
+                    "Expecting number".to_string(),
+                )),
             },
             CalcResult::Boolean(f) => {
                 if f {
@@ -108,24 +114,13 @@ impl Model {
     ) -> Result<f64, CalcResult> {
         match result {
             CalcResult::Number(f) => Ok(f),
-            CalcResult::String(s) => match s.trim().parse::<f64>() {
-                Ok(f) => Ok(f),
-                _ => {
-                    let mut currencies = vec!["$", "€"];
-                    let currency = &self.locale.currency.symbol;
-                    if !currencies.iter().any(|e| e == currency) {
-                        currencies.push(currency);
-                    }
-                    // Try to parse as a formatted number (e.g., dates, currencies, percentages)
-                    if let Ok((v, _number_format)) = parse_formatted_number(&s, &currencies) {
-                        return Ok(v);
-                    }
-                    Err(CalcResult::new_error(
-                        Error::VALUE,
-                        cell,
-                        "Expecting number".to_string(),
-                    ))
-                }
+            CalcResult::String(s) => match self.cast_number(&s) {
+                Some(f) => Ok(f),
+                None => Err(CalcResult::new_error(
+                    Error::VALUE,
+                    cell,
+                    "Expecting number".to_string(),
+                )),
             },
             CalcResult::Boolean(f) => {
                 if f {
diff --git a/base/src/functions/macros.rs b/base/src/functions/macros.rs
index 378aa18..336954f 100644
--- a/base/src/functions/macros.rs
+++ b/base/src/functions/macros.rs
@@ -68,14 +68,14 @@ macro_rules! single_number_fn {
                                 },
                                 // If String, parse to f64 then apply or #VALUE! error
                                 ArrayNode::String(s) => {
-                                    let node = match s.parse::<f64>() {
-                                        Ok(f) => match $op(f) {
+                                    let node = match self.cast_number(&s) {
+                                        Some(f) => match $op(f) {
                                             Ok(x) => ArrayNode::Number(x),
                                             Err(Error::DIV) => ArrayNode::Error(Error::DIV),
                                             Err(Error::VALUE) => ArrayNode::Error(Error::VALUE),
                                             Err(e) => ArrayNode::Error(e),
                                         },
-                                        Err(_) => ArrayNode::Error(Error::VALUE),
+                                        None => ArrayNode::Error(Error::VALUE),
                                     };
                                     data_row.push(node);
                                 }
diff --git a/base/src/functions/mathematical.rs b/base/src/functions/mathematical.rs
index 057fff6..025e109 100644
--- a/base/src/functions/mathematical.rs
+++ b/base/src/functions/mathematical.rs
@@ -1336,7 +1336,13 @@ impl Model {
         }
         Ok(acc)
     });
-    single_number_fn!(fn_sign, |f| Ok(f64::signum(f)));
+    single_number_fn!(fn_sign, |f| {
+        if f == 0.0 {
+            Ok(0.0)
+        } else {
+            Ok(f64::signum(f))
+        }
+    });
     single_number_fn!(fn_degrees, |f| Ok(f * (180.0 / PI)));
     single_number_fn!(fn_radians, |f| Ok(f * (PI / 180.0)));
     single_number_fn!(fn_odd, |f| {
diff --git a/xlsx/tests/calc_tests/EXP_SIGN.xlsx b/xlsx/tests/calc_tests/EXP_SIGN.xlsx
new file mode 100644
index 0000000..6774bdd
Binary files /dev/null and b/xlsx/tests/calc_tests/EXP_SIGN.xlsx differ