WPF , can not set 0 in my slider Max and Min fixed

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Visual-Studio

WPF

C#5.0

I tried modifing the frecuency of my slider but still I can not set value 0 on my slider and I don't understand why. In the SliderToolTip appears.

<Label TextOptions.TextFormattingMode="Ideal" Width="140" Foreground="#2B3856" FontWeight="Bold" FontSize="16"   Margin="3">Tide Height </Label>
<Slider HorizontalAlignment="Left" x:Name="tideHeight_11"
                     Margin="3"
                     VerticalAlignment="Top"
                     Width="250"
                    Minimum="-12.4" Maximum="12.4"  IsSnapToTickEnabled="True" TickFrequency="1<big></big>" AutoToolTipPlacement="BottomRight" ValueChanged="Slider_ValueChanged"/>
 <TextBlock TextOptions.TextFormattingMode="Ideal" Width="50" Foreground="#2B3856" FontSize="16" x:Name="tideHeightText" Text="{Binding Value, ElementName=tideHeight_11}" >
</TextBlock>

Any help please?