How do I take two user inputs (Subject Grade and Units) and store it in two different arrays?

Question

I want the program to prompt the user in entering their grade and the unit for that subject. Using nested for loops, I wished to simultaneously get this 2 input simultaneously per subject:

    Scanner userInput = new Scanner(System.in);

    //Initializing variables and array

    double[] userGrades = new double[10];
    double[] userUnits = new double[10];

    int subjectCounter = 1;
    


    // Nested for Loop to get each grade and units per subject
    for(int i = 0; i < userGrades.length; ++i){

        System.out.println("\nEnter your grade for Subject " + subjectCounter + ": ");
        userGrades[i] = userInput.nextDouble();
        
        subjectCounter++;

        for(int j = 0; j <= i; ++j){
            System.out.println("Enter the number of units:");
            userUnits[j] = userInput.nextDouble();
        }
    }

The output for this prompt is:

Enter Grade for Subject 1:

Enter Unit for Subject 1:

Enter Grade for Subject 2:

Enter Unit for Subject 2:

...

When I check the elements of userGrades[], it outputs the grades of every subject which is what I want. But when I check the elements of userUnits[], it outputs 9 zeroes, and the last number I typed for "Enter Units for this Subject: " (which is in Subject 10).

Why do userGrades[] store the correct elements while userUnits[] does not? I need help as I just started learning nested for loops and arrays.