diff --git a/cpdfcommand.ml b/cpdfcommand.ml
index c68b4ef..e6845d8 100644
--- a/cpdfcommand.ml
+++ b/cpdfcommand.ml
@@ -749,23 +749,12 @@ let cropbox pdf page =
   | Some pdfobject -> Pdf.direct pdf pdfobject
   | None -> page.Pdfpage.mediabox
 
-let width box =
-  let minx, miny, maxx, maxy = Pdf.parse_rectangle box in maxx -. minx
-
-let height box =
-  let minx, miny, maxx, maxy = Pdf.parse_rectangle box in maxy -. miny
-
-let minx box =
-  let minx, miny, maxx, maxy = Pdf.parse_rectangle box in minx
-
-let miny box =
-  let minx, miny, maxx, maxy = Pdf.parse_rectangle box in miny
-
-let maxx box =
-  let minx, miny, maxx, maxy = Pdf.parse_rectangle box in maxx
-
-let maxy box =
-  let minx, miny, maxx, maxy = Pdf.parse_rectangle box in maxy
+let width box = let minx, miny, maxx, maxy = Pdf.parse_rectangle box in maxx -. minx
+let height box = let minx, miny, maxx, maxy = Pdf.parse_rectangle box in maxy -. miny
+let minx box = let minx, miny, maxx, maxy = Pdf.parse_rectangle box in minx
+let miny box = let minx, miny, maxx, maxy = Pdf.parse_rectangle box in miny
+let maxx box = let minx, miny, maxx, maxy = Pdf.parse_rectangle box in maxx
+let maxy box = let minx, miny, maxx, maxy = Pdf.parse_rectangle box in maxy
 
 let find_page_width pdf page = width page.Pdfpage.mediabox
 let find_page_height pdf page = height page.Pdfpage.mediabox
diff --git a/cpdfmanual.pdf b/cpdfmanual.pdf
index 36de6a2..e652f85 100644
Binary files a/cpdfmanual.pdf and b/cpdfmanual.pdf differ
diff --git a/cpdfmanual.tex b/cpdfmanual.tex
index 5e16bcf..fccf8c4 100644
--- a/cpdfmanual.tex
+++ b/cpdfmanual.tex
@@ -276,13 +276,37 @@ supported:
 \begin{table}[h]
 \centering
 \begin{tabular}{rl}
-  pt & Points (72 points per inch). The default. \\
-  cm & Centimeters \\
-  mm & Millimeters \\
-  in & Inches \\
+  \texttt{pt} & Points (72 points per inch). The default. \\
+  \texttt{cm} & Centimeters \\
+  \texttt{mm} & Millimeters \\
+  \texttt{in} & Inches \\
 \end{tabular}
 \end{table}
 
+\noindent For example, one may write \texttt{14mm} or \texttt{21.6in}. In addition, the following letters stand, in some operations (\texttt{-scale-page}, \texttt{-scale-to-fit}, \texttt{-scale-contents}, \texttt{-shift}, \texttt{-mediabox}, \texttt{-crop}) for various page dimensions:
+
+\begin{table}[h]
+\centering
+\begin{tabular}{rl}
+  \texttt{PW} & Page width\\
+  \texttt{PH} & Page height\\
+  \texttt{PMINX} & Page minimum x coordinate\\
+  \texttt{PMINY} & Page minimum y coordinate\\
+  \texttt{PMAXX} & Page maximum x coordinate\\
+  \texttt{PMAXY} & Page maximum y coordinate\\
+  \texttt{CW} & Crop box width\\
+  \texttt{CH} & Crop box height\\
+  \texttt{CMINX} & Crop box minimum x coordinate\\
+  \texttt{CMINY} & Crop box minimum y coordinate\\
+  \texttt{CMAXX} & Crop box maximum x coordinate\\
+  \texttt{CMAXY} & Crop box maximum y coordinate
+\end{tabular}
+\end{table}
+
+\noindent For example, we may write \texttt{PMINX PMINY} to stand for the coordinate of the lower left corner of the page.
+
+Simple arithmetic may be performed using the words \texttt{add}, \texttt{sub}, \texttt{mul} and \texttt{div} to stand for addition, subtraction, multiplication and division. For example, one may write \texttt{14in sub 30pt} or \texttt{PMINX mul 2}
+
 \section{PDF Version Numbers}
 \index{version number}
 When an operation which uses a part of the PDF standard which was introduced in