diff --git a/rinex/src/header.rs b/rinex/src/header.rs
index 1cf330381..cde89e601 100644
--- a/rinex/src/header.rs
+++ b/rinex/src/header.rs
@@ -1610,11 +1610,14 @@ impl Header {
                     /*
                      * List of observables
                      */
-                    for (constell, observables) in &obs.codes {
+                    for (index, (constell, observables)) in obs.codes.iter().enumerate() {
                         let mut descriptor = String::new();
                         descriptor.push_str(&format!("{:x}{:5}", constell, observables.len()));
-                        for observable in observables {
-                            descriptor.push_str(&format!(" {}", observable));
+                        for (i, observable) in observables.iter().enumerate() {
+                            if (i % 13) == 0 && (i > 0) {
+                                descriptor.push_str(&format!("        ")); // TAB
+                            }
+                            descriptor.push_str(&format!(" {}", observable)); // TAB
                         }
                         writeln!(f, "{}", fmt_rinex(&descriptor, "SYS / # / OBS TYPES"))?;
                     }
diff --git a/rinex/src/lib.rs b/rinex/src/lib.rs
index d604f4e2d..c3282a2da 100644
--- a/rinex/src/lib.rs
+++ b/rinex/src/lib.rs
@@ -147,12 +147,9 @@ pub(crate) fn fmt_rinex(content: &str, marker: &str) -> String {
         for i in 0..nb_lines {
             let start_off = i * 60;
             let end_off = std::cmp::min(start_off + 60, content.len());
-            string.push_str(&format!(
-                "{:<padding$}{}",
-                &content[start_off..end_off],
-                marker,
-                padding = 60
-            ));
+            let chunk = &content[start_off..end_off];
+            let len = chunk.len();
+            string.push_str(&format!("{:<padding$}{}", chunk, marker, padding = 60));
             if i < nb_lines - 1 {
                 string.push('\n');
             }
@@ -3471,4 +3468,16 @@ mod test {
             }
         }
     }
+    #[test]
+    fn fmt_observables_v3() {
+        for (desc, expected) in [
+("R    9 C1C L1C S1C C2C C2P L2C L2P S2C S2P",
+"R    9 C1C L1C S1C C2C C2P L2C L2P S2C S2P                  SYS / # / OBS TYPES"),
+("G   18 C1C L1C S1C C2P C2W C2S C2L C2X L2P L2W L2S L2L L2X         S2P S2W S2S S2L S2X",
+"G   18 C1C L1C S1C C2P C2W C2S C2L C2X L2P L2W L2S L2L L2X  SYS / # / OBS TYPES
+       S2P S2W S2S S2L S2X                                  SYS / # / OBS TYPES"),
+        ] {
+            assert_eq!(fmt_rinex(desc, "SYS / # / OBS TYPES"), expected);
+        }
+    }
 }
diff --git a/rinex/src/tests/production.rs b/rinex/src/tests/production.rs
index a7c42b939..deb0a9c39 100644
--- a/rinex/src/tests/production.rs
+++ b/rinex/src/tests/production.rs
@@ -4,7 +4,7 @@ mod test {
     use crate::*;
     use std::path::Path;
     fn testbench(path: &str) {
-        // parse this file
+        println!("running on \"{}\"", path);
         let rnx = Rinex::from_file(path).unwrap(); // already tested elsewhere
         let tmp_path = format!("test-{}.rnx", random_name(5));
         assert!(rnx.to_file(&tmp_path).is_ok()); // test writer