diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/AlarmCommand.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/AlarmCommand.java
index a351920b4..b443eb6fb 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/AlarmCommand.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/AlarmCommand.java
@@ -131,13 +131,13 @@ public class AlarmCommand extends BaseCommand {
     protected void deserializeParams(byte id, ByteBuffer params) {
         validateId(id, LefunConstants.CMD_ALARM);
 
-        if (params.limit() < 2)
+        if (params.limit() - params.position() < 2)
             throwUnexpectedLength();
 
         op = params.get();
         index = params.get();
         if (op == OP_GET) {
-            if (params.limit() != 8)
+            if (params.limit() - params.position() != 8)
                 throwUnexpectedLength();
 
             enabled = params.get() == 1;
@@ -147,7 +147,7 @@ public class AlarmCommand extends BaseCommand {
             hour = params.get();
             minute = params.get();
         } else if (op == OP_SET) {
-            if (params.limit() != 3)
+            if (params.limit() - params.position() != 3)
                 throwUnexpectedLength();
 
             setSuccess = params.get() == 1;
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/BaseCommand.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/BaseCommand.java
index 486dc0b25..2a90fbcb2 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/BaseCommand.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/BaseCommand.java
@@ -49,20 +49,20 @@ public abstract class BaseCommand {
         return makeCommand(id, buffer);
     }
 
-    static protected byte calculateChecksum(byte[] data, int offset, int length) {
-        byte checksum = 0;
+    public static byte calculateChecksum(byte[] data, int offset, int length) {
+        int checksum = 0;
         for (int i = offset; i < offset + length; ++i) {
             byte b = data[i];
             for (int j = 0; j < 8; ++j) {
                 if (((b ^ checksum) & 1) == 0) {
                     checksum >>= 1;
                 } else {
-                    checksum = (byte) ((checksum ^ 0x18) >> 1 | 0x80);
+                    checksum = (checksum ^ 0x18) >> 1 | 0x80;
                 }
                 b >>= 1;
             }
         }
-        return checksum;
+        return (byte)checksum;
     }
 
     /**
@@ -98,7 +98,7 @@ public abstract class BaseCommand {
 
     protected void validateIdAndLength(byte id, ByteBuffer params, byte expectedId, int expectedLength) {
         validateId(id, expectedId);
-        if (params.limit() != expectedLength)
+        if (params.limit() - params.position() != expectedLength)
             throwUnexpectedLength();
     }
 
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/Cmd22Command.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/Cmd22Command.java
index c40a92fc3..2cd78b5a3 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/Cmd22Command.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/Cmd22Command.java
@@ -54,17 +54,17 @@ public class Cmd22Command extends BaseCommand {
     protected void deserializeParams(byte id, ByteBuffer params) {
         validateId(id, LefunConstants.CMD_UNKNOWN_22);
 
-        if (params.limit() < 1)
+        if (params.limit() - params.position() < 1)
             throwUnexpectedLength();
 
         op = params.get();
         if (op == OP_GET) {
-            if (params.limit() != 3)
+            if (params.limit() - params.position() != 3)
                 throwUnexpectedLength();
 
             unknown = params.getShort();
         } else if (op == OP_SET) {
-            if (params.limit() != 2)
+            if (params.limit() - params.position() != 2)
                 throwUnexpectedLength();
 
             setSuccess = params.get() == 1;
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/Cmd25Command.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/Cmd25Command.java
index 9bc49813d..e90f5a410 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/Cmd25Command.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/Cmd25Command.java
@@ -56,17 +56,17 @@ public class Cmd25Command extends BaseCommand {
     protected void deserializeParams(byte id, ByteBuffer params) {
         validateId(id, LefunConstants.CMD_UNKNOWN_25);
 
-        if (params.limit() < 1)
+        if (params.limit() - params.position() < 1)
             throwUnexpectedLength();
 
         op = params.get();
         if (op == OP_GET) {
-            if (params.limit() != 5)
+            if (params.limit() - params.position() != 5)
                 throwUnexpectedLength();
 
             unknown = params.getInt();
         } else if (op == OP_SET) {
-            if (params.limit() != 2)
+            if (params.limit() - params.position() != 2)
                 throwUnexpectedLength();
 
             setSuccess = params.get() == 1;
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/FeaturesCommand.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/FeaturesCommand.java
index b0006d4ed..22c5fba2c 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/FeaturesCommand.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/FeaturesCommand.java
@@ -65,17 +65,17 @@ public class FeaturesCommand extends BaseCommand {
     protected void deserializeParams(byte id, ByteBuffer params) {
         validateId(id, LefunConstants.CMD_FEATURES);
 
-        if (params.limit() < 1)
+        if (params.limit() - params.position() < 1)
             throwUnexpectedLength();
 
         op = params.get();
         if (op == OP_GET) {
-            if (params.limit() != 3)
+            if (params.limit() - params.position() != 3)
                 throwUnexpectedLength();
 
             features = params.getShort();
         } else if (op == OP_SET) {
-            if (params.limit() != 2)
+            if (params.limit() - params.position() != 2)
                 throwUnexpectedLength();
 
             setSuccess = params.get() == 1;
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/GetPpgDataCommand.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/GetPpgDataCommand.java
index 25a812944..d17c4b0c6 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/GetPpgDataCommand.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/GetPpgDataCommand.java
@@ -66,7 +66,7 @@ public class GetPpgDataCommand extends BaseCommand {
     protected void deserializeParams(byte id, ByteBuffer params) {
         validateId(id, LefunConstants.CMD_PPG_DATA);
 
-        if (params.limit() < 9)
+        if (params.limit() - params.position() < 9)
             throwUnexpectedLength();
 
         ppgType = params.get();
@@ -93,19 +93,19 @@ public class GetPpgDataCommand extends BaseCommand {
                 throw new IllegalArgumentException("Unknown PPG type");
         }
 
-        if (params.limit() < dataLength + 9)
+        if (params.limit() - params.position() < dataLength + 9)
             throwUnexpectedLength();
 
         ppgData = new byte[dataLength];
         params.get(ppgData);
 
         // Extended count/index
-        if (params.limit() == dataLength + 11)
+        if (params.limit() - params.position() == dataLength + 11)
         {
             totalRecords |= params.get() << 8;
             currentRecord |= params.get() << 8;
         }
-        else if (params.limit() > dataLength + 11) {
+        else if (params.limit() - params.position() > dataLength + 11) {
             throwUnexpectedLength();
         }
     }
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/HydrationReminderIntervalCommand.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/HydrationReminderIntervalCommand.java
index e92fa8aee..801d90fb2 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/HydrationReminderIntervalCommand.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/HydrationReminderIntervalCommand.java
@@ -56,17 +56,17 @@ public class HydrationReminderIntervalCommand extends BaseCommand {
     protected void deserializeParams(byte id, ByteBuffer params) {
         validateId(id, LefunConstants.CMD_HYDRATION_REMINDER_INTERVAL);
 
-        if (params.limit() < 1)
+        if (params.limit() - params.position() < 1)
             throwUnexpectedLength();
 
         op = params.get();
         if (op == OP_GET) {
-            if (params.limit() != 2)
+            if (params.limit() - params.position() != 2)
                 throwUnexpectedLength();
 
             hydrationReminderInterval = params.get();
         } else if (op == OP_SET) {
-            if (params.limit() != 2)
+            if (params.limit() - params.position() != 2)
                 throwUnexpectedLength();
 
             setSuccess = params.get() == 1;
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/PpgResultCommand.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/PpgResultCommand.java
index 0a55a54a8..c4d89e7f5 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/PpgResultCommand.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/PpgResultCommand.java
@@ -38,7 +38,7 @@ public class PpgResultCommand extends BaseCommand {
     protected void deserializeParams(byte id, ByteBuffer params) {
         validateId(id, LefunConstants.CMD_PPG_RESULT);
 
-        if (params.limit() < 1)
+        if (params.limit() - params.position() < 1)
             throwUnexpectedLength();
 
         ppgType = params.get();
@@ -57,7 +57,7 @@ public class PpgResultCommand extends BaseCommand {
                 throw new IllegalArgumentException("Unknown PPG type");
         }
 
-        if (params.limit() != dataLength + 1)
+        if (params.limit() - params.position() != dataLength + 1)
             throwUnexpectedLength();
 
         ppgData = new byte[dataLength];
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/ProfileCommand.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/ProfileCommand.java
index e4b806108..dc8910c89 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/ProfileCommand.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/ProfileCommand.java
@@ -94,12 +94,12 @@ public class ProfileCommand extends BaseCommand {
     protected void deserializeParams(byte id, ByteBuffer params) {
         validateId(id, LefunConstants.CMD_PROFILE);
 
-        if (params.limit() < 1)
+        if (params.limit() - params.position() < 1)
             throwUnexpectedLength();
 
         op = params.get();
         if (op == OP_GET) {
-            if (params.limit() != 5)
+            if (params.limit() - params.position() != 5)
                 throwUnexpectedLength();
 
             gender = params.get();
@@ -107,7 +107,7 @@ public class ProfileCommand extends BaseCommand {
             weight = params.get();
             age = params.get();
         } else if (op == OP_SET) {
-            if (params.limit() != 2)
+            if (params.limit() - params.position() != 2)
                 throwUnexpectedLength();
 
             setSuccess = params.get() == 1;
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/SedentaryReminderIntervalCommand.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/SedentaryReminderIntervalCommand.java
index fa116134d..fcf43a255 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/SedentaryReminderIntervalCommand.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/SedentaryReminderIntervalCommand.java
@@ -56,17 +56,17 @@ public class SedentaryReminderIntervalCommand extends BaseCommand {
     protected void deserializeParams(byte id, ByteBuffer params) {
         validateId(id, LefunConstants.CMD_SEDENTARY_REMINDER_INTERVAL);
 
-        if (params.limit() < 1)
+        if (params.limit() - params.position() < 1)
             throwUnexpectedLength();
 
         op = params.get();
         if (op == OP_GET) {
-            if (params.limit() != 2)
+            if (params.limit() - params.position() != 2)
                 throwUnexpectedLength();
 
             sedentaryReminderInterval = params.get();
         } else if (op == OP_SET) {
-            if (params.limit() != 2)
+            if (params.limit() - params.position() != 2)
                 throwUnexpectedLength();
 
             setSuccess = params.get() == 1;
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/SettingsCommand.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/SettingsCommand.java
index 1c76a8711..f0828a7d9 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/SettingsCommand.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/SettingsCommand.java
@@ -83,19 +83,19 @@ public class SettingsCommand extends BaseCommand {
     protected void deserializeParams(byte id, ByteBuffer params) {
         validateId(id, LefunConstants.CMD_SETTINGS);
 
-        if (params.limit() < 1)
+        if (params.limit() - params.position() < 1)
             throwUnexpectedLength();
 
         op = params.get();
         if (op == OP_GET) {
-            if (params.limit() != 4)
+            if (params.limit() - params.position() != 4)
                 throwUnexpectedLength();
 
             option1 = params.get();
             amPmIndicator = params.get();
             measurementUnit = params.get();
         } else if (op == OP_SET) {
-            if (params.limit() != 2)
+            if (params.limit() - params.position() != 2)
                 throwUnexpectedLength();
 
             setSuccess = params.get() == 1;
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/TimeCommand.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/TimeCommand.java
index f25a6c27f..7c35a22ad 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/TimeCommand.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/TimeCommand.java
@@ -109,12 +109,12 @@ public class TimeCommand extends BaseCommand {
     protected void deserializeParams(byte id, ByteBuffer params) {
         validateId(id, LefunConstants.CMD_TIME);
 
-        if (params.limit() < 1)
+        if (params.limit() - params.position() < 1)
             throwUnexpectedLength();
 
         op = params.get();
         if (op == OP_GET) {
-            if (params.limit() != 7)
+            if (params.limit() - params.position() != 7)
                 throwUnexpectedLength();
 
             year = params.get();
@@ -124,7 +124,7 @@ public class TimeCommand extends BaseCommand {
             minute = params.get();
             second = params.get();
         } else if (op == OP_SET) {
-            if (params.limit() != 2)
+            if (params.limit() - params.position() != 2)
                 throwUnexpectedLength();
 
             setSuccess = params.get() == 1;
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/UiPagesCommand.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/UiPagesCommand.java
index 77deae3cc..3c2e595c5 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/UiPagesCommand.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/devices/lefun/commands/UiPagesCommand.java
@@ -61,17 +61,17 @@ public class UiPagesCommand extends BaseCommand {
     protected void deserializeParams(byte id, ByteBuffer params) {
         validateId(id, LefunConstants.CMD_UI_PAGES);
 
-        if (params.limit() < 1)
+        if (params.limit() - params.position() < 1)
             throwUnexpectedLength();
 
         op = params.get();
         if (op == OP_GET) {
-            if (params.limit() != 3)
+            if (params.limit() - params.position() != 3)
                 throwUnexpectedLength();
 
             pages = params.getShort();
         } else if (op == OP_SET) {
-            if (params.limit() != 2)
+            if (params.limit() - params.position() != 2)
                 throwUnexpectedLength();
 
             setSuccess = params.get() == 1;