user13665: I am reading a book on chess openings called 51 Chess Openings for Beginners by Bruce Albertson and the author uses notation like so:


...†† Kxf7


What does the †† mean? I know a single † means check however the author doesn't (to my knowledge) explain what the †† is meant to signify.
EDIT: here's a screenshot to provide some context of its usage 



user12629: If † means check, then †† means a double check.  A double check is when two pieces give check at the same time.  For example:
[White "NN"]
[Black "NN"]
[FEN "7k/8/5Rpn/8/3Q4/8/8/7K w - - 0 1"]
[SetUp "1"]
[CurrentPosition "6nk/5N2/6K1/8/8/8/8/8 b - - 1 2"]

1.Rf8++

If this does not apply to the position in question, then you should know that †† is sometimes generically used to indicate a footnote.

user13433: Well, after your update I come to the conclusion that these signs are used by the author to mark the omission of the notation of the respective move by White. 
This is not a common usage of them, and I have never seen it before. It should be documented somewhere at the beginning or end of the book. But I'd not be surprised  if it's not, since it doesn't reflect a healthy common sense to use the check symbol of all things for this purpose to begin with..

13665: <p>I am reading a book on chess openings called <em>51 Chess Openings for Beginners by Bruce Albertson</em> and the author uses notation like so:</p>

<blockquote>
  <ol start="6">
  <li>...†† Kxf7</li>
  </ol>
</blockquote>

<p>What does the <code>††</code> mean? I know a single <code>†</code> means <em>check</em> however the author doesn't (to my knowledge) explain what the <code>††</code> is meant to signify.</p>

<p><strong>EDIT</strong>: here's a screenshot to provide some context of its usage </p>

<p><a href="https://i.stack.imgur.com/dCQhn.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/dCQhn.png" alt="excerpt from chess book"></a>
<a href="https://i.stack.imgur.com/Qtdb6.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Qtdb6.png" alt="the next page"></a></p>
 12629: <p>If † means check, then †† means a double check.  A double check is when two pieces give check at the same time.  For example:</p>

<pre><code>[White "NN"]
[Black "NN"]
[FEN "7k/8/5Rpn/8/3Q4/8/8/7K w - - 0 1"]
[SetUp "1"]
[CurrentPosition "6nk/5N2/6K1/8/8/8/8/8 b - - 1 2"]

1.Rf8++
</code></pre>

<p>If this does not apply to the position in question, then you should know that †† is sometimes generically used to indicate a footnote.</p>
 13433: <p>Well, after your update I come to the conclusion that these signs are used by the author to mark the omission of the notation of the respective move by White. </p>

<p>This is not a common usage of them, and I have never seen it before. It <em>should</em> be documented somewhere at the beginning or end of the book. But I'd not be surprised  if it's not, since it doesn't reflect a healthy common sense to use the check symbol of all things for this purpose to begin with..</p>
