diff --git a/lib/libx52/Makefile.am b/lib/libx52/Makefile.am
index 7ecac03..ea15b66 100644
--- a/lib/libx52/Makefile.am
+++ b/lib/libx52/Makefile.am
@@ -30,6 +30,15 @@ x52include_HEADERS = libx52.h
 # pkg-config files
 pkgconfig_DATA = libx52.pc
 
+check_PROGRAMS = test_offset
+
+test_offset_SOURCES = test_offset.c
+test_offset_CFLAGS = @LIBUSB_CFLAGS@
+test_offset_LDADD = libx52.la
+
+LOG_DRIVER = env AM_TAP_AWK='$(AWK)' $(SHELL) $(top_srcdir)/tap-driver.sh
+TESTS = test_offset
+
 # Extra files that need to be in the distribution
 EXTRA_DIST = libx52.h x52_commands.h x52_common.h README.md
 
diff --git a/lib/libx52/test_offset.c b/lib/libx52/test_offset.c
new file mode 100644
index 0000000..930a81d
--- /dev/null
+++ b/lib/libx52/test_offset.c
@@ -0,0 +1,69 @@
+/*
+ * Saitek X52 Pro MFD & LED driver
+ * Test program for validating offset calculation
+ *
+ * Copyright (C) 2020 Nirenjan Krishnan (nirenjan@nirenjan.org)
+ *
+ * SPDX-License-Identifier: GPL-2.0-only WITH Classpath-exception-2.0
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+#include "x52_common.h"
+
+struct test_id {
+    const char *test_case_id;
+    int offset_primary;
+    int offset_secondary;
+    uint16_t x52_offset;
+};
+
+const struct test_id test_cases[] = {
+    {"Etc/UTC+24|Etc/UTC-24", -1440, +1440, 0},
+    {"Etc/UTC-24|Etc/UTC+24", +1440, -1440, 0x0400}, // Negative 0
+    {"Honolulu|Auckland", -600, +720, 0x0478}, // -2 hours
+    {"Auckland|Honolulu", +720, -600, 0x0078}, // +2 hours
+    {"Etc/UTC+12|Etc/UTC-14", -720, +840, 0x078}, // +2 hours
+    {"Etc/UTC-14|Etc/UTC+12", +840, -720, 0x478}, // -2 hours
+    {"PDT|UTC", -420, 0, 0x1a4}, // +7 hours
+    {"UTC|PDT", 0, -420, 0x5a4}, // -7 hours
+    {"PST|UTC", -480, 0, 0x1e0}, // +8 hours
+    {"UTC|PST", 0, -480, 0x5e0}, // -8 hours
+    {"Etc/UTC+12|Etc/UTC-12", -720, +720, 0},
+    {"Etc/UTC-12|Etc/UTC+12", +720, -720, 0x0400},
+};
+
+#define TC_COUNT (sizeof(test_cases) / sizeof(test_cases[0]))
+
+void run_test(int tc_id)
+{
+    struct libx52_device dev;
+    memset(&dev, 0, sizeof(dev));
+
+    struct test_id test = test_cases[tc_id];
+
+    dev.timezone[LIBX52_CLOCK_1] = test.offset_primary;
+    dev.timezone[LIBX52_CLOCK_2] = test.offset_secondary;
+
+    uint16_t obtained = libx52_calculate_clock_offset(&dev, LIBX52_CLOCK_2, 0);
+    if (obtained != test.x52_offset) {
+        printf("not ");
+    }
+    printf("ok %d %s\n", tc_id + 1, test.test_case_id);
+    if (obtained != test.x52_offset) {
+        // Diagnostics
+        printf("# Expected: %04x\n", test.x52_offset);
+        printf("# Observed: %04x\n", obtained);
+    }
+}
+
+int main()
+{
+    int i;
+
+    printf("1..%ld\n", TC_COUNT);
+    for (i = 0; i < TC_COUNT; i++) {
+        run_test(i);
+    }
+}
diff --git a/lib/libx52/x52_common.h b/lib/libx52/x52_common.h
index c3e8533..8928a9a 100644
--- a/lib/libx52/x52_common.h
+++ b/lib/libx52/x52_common.h
@@ -105,5 +105,6 @@ static inline uint32_t tst_bit(uint32_t *value, uint32_t bit)
 }
 
 int _x52_translate_libusb_error(enum libusb_error errcode);
+uint16_t libx52_calculate_clock_offset(libx52_device *x52, libx52_clock_id clock, uint16_t h24);
 
 #endif /* !defined X52JOY_COMMON_H */
diff --git a/lib/libx52/x52_control.c b/lib/libx52/x52_control.c
index 655aca5..e96db59 100644
--- a/lib/libx52/x52_control.c
+++ b/lib/libx52/x52_control.c
@@ -209,7 +209,7 @@ static int _x52_write_date(libx52_device *x52, uint32_t bit)
     return rc;
 }
 
-int _x52_calculate_clock_offset(libx52_device *x52, libx52_clock_id clock, uint16_t h24)
+uint16_t libx52_calculate_clock_offset(libx52_device *x52, libx52_clock_id clock, uint16_t h24)
 {
     int offset;
     int negative;
@@ -231,7 +231,7 @@ int _x52_calculate_clock_offset(libx52_device *x52, libx52_clock_id clock, uint1
      * greater issue is to take the two extreme timezones at -1200 and +1400
      * for a difference of +26 hours. The safe bet is to check if the offset
      * exceeds +/- 1023, and subtract 1440, which will convert the offset of
-     * +22 to -2 hours, or +26 to +4 hours.
+     * +22 to -2 hours, or +26 to +2 hours.
      */
     while (offset > 1023) {
         offset -= 1440; // Subtract 24 hours
@@ -272,7 +272,7 @@ static int _x52_write_time(libx52_device *x52, uint32_t bit)
     uint16_t h24 = !!(x52->time_format[clock]);
 
     if (clock != LIBX52_CLOCK_1) {
-        value = _x52_calculate_clock_offset(x52, clock, h24);
+        value = libx52_calculate_clock_offset(x52, clock, h24);
     } else {
         value = h24 << 15 |
                 (x52->time_hour & 0x7F) << 8 |