how to use dimens.xml to set text size in android

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XML

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Android4x

hi guys . i am working on an android application .
i wanted to set text size correctly for all android devices , so i decided to use dimens.xml
but unfortunately when i tried to Set text Size , i got an error
Error : No resource found that matches the given name at TextSize with value @dimens/Big

here is my dimens.xml which was defined in /res/value-hdpi/dimens.xml :

<resources>
    <dimen name="Big">70sp</dimen>
</resources>

and this my Xml File :

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Seyed Mahmud Shahrokni"
    android:textSize="@dimens/Big"
    />

any suggestion ?