diff --git a/lib/libx52/Makefile.am b/lib/libx52/Makefile.am
index 39b2bac..7c01736 100644
--- a/lib/libx52/Makefile.am
+++ b/lib/libx52/Makefile.am
@@ -33,7 +33,7 @@ pkgconfig_DATA = libx52.pc
 
 check_PROGRAMS = test_offset test_led test_blink_shift
 
-test_offset_SOURCES = test_offset.c
+test_offset_SOURCES = test_offset.c test_common.c
 test_offset_CFLAGS = @LIBUSB_CFLAGS@
 test_offset_LDADD = libx52.la
 
diff --git a/lib/libx52/test_offset.c b/lib/libx52/test_offset.c
index 930a81d..972c088 100644
--- a/lib/libx52/test_offset.c
+++ b/lib/libx52/test_offset.c
@@ -11,51 +11,74 @@
 #include <stdint.h>
 #include <string.h>
 #include "x52_common.h"
+#include "test_common.h"
 
-struct test_id {
+struct test_case {
     const char *test_case_id;
     int offset_primary;
     int offset_secondary;
+    libx52_clock_id clock_id;
+    uint16_t x52_clock;
     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 TEST(id, o1, o23, offs) {id, o1, o23, LIBX52_CLOCK_2, 0xc1, offs}, {id, o1, o23, LIBX52_CLOCK_3, 0xc2, offs}
+
+const struct test_case test_cases[] = {
+    TEST("Etc/UTC+24|Etc/UTC-24", -1440, +1440, 0),
+    TEST("Etc/UTC-24|Etc/UTC+24", +1440, -1440, 0x0400), // Negative 0
+    TEST("Honolulu|Auckland", -600, +720, 0x0478), // -2 hours
+    TEST("Auckland|Honolulu", +720, -600, 0x0078), // +2 hours
+    TEST("Etc/UTC+12|Etc/UTC-14", -720, +840, 0x078), // +2 hours
+    TEST("Etc/UTC-14|Etc/UTC+12", +840, -720, 0x478), // -2 hours
+    TEST("PDT|UTC", -420, 0, 0x1a4), // +7 hours
+    TEST("UTC|PDT", 0, -420, 0x5a4), // -7 hours
+    TEST("PST|UTC", -480, 0, 0x1e0), // +8 hours
+    TEST("UTC|PST", 0, -480, 0x5e0), // -8 hours
+    TEST("Etc/UTC+12|Etc/UTC-12", -720, +720, 0),
+    TEST("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 libx52_device *dev = x52_test_init();
+    struct test_case test = test_cases[tc_id];
+    int rc;
+    struct ivpair data[2] = { 0 };
 
-    struct test_id test = test_cases[tc_id];
+    #define PRINT_FAIL() printf("not ok %d %s/%d\n", tc_id+1, test.test_case_id, test.clock_id + 1)
+    #define PRINT_PASS() printf("ok %d %s/%d\n", tc_id+1, test.test_case_id, test.clock_id + 1)
 
-    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 ");
+    dev->timezone[LIBX52_CLOCK_1] = test.offset_primary;
+    rc = libx52_set_clock_timezone(dev, test.clock_id, test.offset_secondary);
+    if (rc != LIBX52_SUCCESS) {
+        PRINT_FAIL();
+        printf("# set_clock_timezone failed, rc = %d\n", rc);
+        return;
     }
-    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);
+
+    rc = libx52_update(dev);
+    if (rc != LIBX52_SUCCESS) {
+        PRINT_FAIL();
+        printf("# libx52_update failed, rc = %d\n", rc);
+        return;
     }
+
+    data[0].index = test.x52_clock;
+    data[0].value = test.x52_offset;
+
+    if (!x52_test_assert_expected(dev, data)) {
+        PRINT_FAIL();
+        x52_test_print_diagnostics();
+        x52_test_print_expected_data(data);
+        x52_test_print_observed_data(dev);
+        return;
+    }
+
+    PRINT_PASS();
+    x52_test_cleanup(dev);
 }
 
 int main()
diff --git a/lib/libx52/x52_common.h b/lib/libx52/x52_common.h
index 44e2e22..8916e4a 100644
--- a/lib/libx52/x52_common.h
+++ b/lib/libx52/x52_common.h
@@ -109,6 +109,5 @@ static inline uint32_t tst_bit(uint32_t *value, uint32_t bit)
 
 int _x52_translate_libusb_error(enum libusb_error errcode);
 int _x52_vendor_command(libx52_device *x52, uint16_t index, uint16_t value);
-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 6cbadbb..dc3f0ed 100644
--- a/lib/libx52/x52_control.c
+++ b/lib/libx52/x52_control.c
@@ -218,7 +218,7 @@ static int _x52_write_date(libx52_device *x52, uint32_t bit)
     return rc;
 }
 
-uint16_t libx52_calculate_clock_offset(libx52_device *x52, libx52_clock_id clock, uint16_t h24)
+static uint16_t _x52_calculate_clock_offset(libx52_device *x52, libx52_clock_id clock, uint16_t h24)
 {
     int offset;
     int negative;
@@ -285,7 +285,7 @@ static int _x52_write_time(libx52_device *x52, uint32_t bit)
     h24 = !!(x52->time_format[clock]);
 
     if (clock != LIBX52_CLOCK_1) {
-        value = libx52_calculate_clock_offset(x52, clock, h24);
+        value = _x52_calculate_clock_offset(x52, clock, h24);
     } else {
         value = h24 << 15 |
                 (x52->time_hour & 0x7F) << 8 |