Macropod's recommendation should work if you are using the built in heading styles.

The alternative is to use a combination of a styleref field and the equation numbering field. Use the \s switch in the equation numbering field to restart numbering at the relevant heading level.

{styleref "myHeadingstyle2" \s} -{seq equation \s 2}


In Section

3.2 <Title in heading style 2>

<equation 1> {styleref "Heading 2" \s} -{seq equation \s 2}

<equation 2> {styleref "Heading 2" \s} -{seq equation \s 2}

<equation 2> {styleref "Heading 2" \s} -{seq equation \s 2}

Should give you

<equation 1> 3.2-1

<equation 2> 3.2-2

<equation 2> 3.2-3

The \s switch isn't documented and I found it by accident. It appears to insert the chapter number without any preceding text