diff --git a/src/app/main.cpp b/src/app/main.cpp
index 67d0dd3..92fda89 100644
--- a/src/app/main.cpp
+++ b/src/app/main.cpp
@@ -278,6 +278,24 @@ int main(int argc, char** argv) {
                     capture.blocks.size(), capture.seeds.size());
         for (const auto& kv : capture.meta)
             std::printf("  %s: %s\n", kv.first.c_str(), kv.second.c_str());
+        // A CAPTURE BELONGS TO ONE SAVE. Replaying a turn's commands against a different board
+        // is not an error the arithmetic can see -- the blocks name player ids that exist in
+        // both, so it charges the counter happily and produces a confident wrong number. When
+        // the capture records which save it was taken on, check it.
+        if (const std::string* bound = capture.Meta("input")) {
+            const std::string want = bound->substr(0, bound->find(' '));
+            std::string have = in;
+            const std::size_t slash = have.find_last_of("/\\");
+            if (slash != std::string::npos) have = have.substr(slash + 1);
+            if (!want.empty() && want != have)
+                std::printf("turn-commands: ! this capture was taken on '%s' and is being "
+                            "replayed against '%s'. A capture belongs to ONE board; the counter "
+                            "will be charged either way and the number will be wrong.\n",
+                            want.c_str(), have.c_str());
+        } else {
+            std::printf("turn-commands: ! this capture does not record which save it was taken "
+                        "on, so nothing here can tell whether it belongs to this one\n");
+        }
     }
     // Seeds given on the command line win over the ones in the file, and a seed for a client the
     // file does not mention is added. Nothing consumes them yet, so this is bookkeeping with a