diff --git a/include/libdivecomputer/hw_frog.h b/include/libdivecomputer/hw_frog.h
index 8698265..3d59445 100644
--- a/include/libdivecomputer/hw_frog.h
+++ b/include/libdivecomputer/hw_frog.h
@@ -31,6 +31,9 @@
 extern "C" {
 #endif /* __cplusplus */
 
+#define HW_FROG_DISPLAY_SIZE    15
+#define HW_FROG_CUSTOMTEXT_SIZE 13
+
 dc_status_t
 hw_frog_device_open (dc_device_t **device, dc_context_t *context, const char *name);
 
diff --git a/include/libdivecomputer/hw_ostc.h b/include/libdivecomputer/hw_ostc.h
index 76271ca..6e0a8c8 100644
--- a/include/libdivecomputer/hw_ostc.h
+++ b/include/libdivecomputer/hw_ostc.h
@@ -31,6 +31,9 @@
 extern "C" {
 #endif /* __cplusplus */
 
+#define HW_OSTC_MD2HASH_SIZE 18
+#define HW_OSTC_EEPROM_SIZE  256
+
 typedef enum hw_ostc_format_t {
 	HW_OSTC_FORMAT_RAW,
 	HW_OSTC_FORMAT_RGB16,
diff --git a/include/libdivecomputer/suunto_eon.h b/include/libdivecomputer/suunto_eon.h
index 8bde22d..31d8c7d 100644
--- a/include/libdivecomputer/suunto_eon.h
+++ b/include/libdivecomputer/suunto_eon.h
@@ -30,6 +30,8 @@
 extern "C" {
 #endif /* __cplusplus */
 
+#define SUUNTO_EON_NAME_SIZE 20
+
 dc_status_t
 suunto_eon_device_open (dc_device_t **device, dc_context_t *context, const char *name);