/usr/share/calc/help/strerror is in apcalc-common 2.12.4.4-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 | NAME
    strerror - returns a string describing an error value
SYNOPSIS
    strerror([x])
TYPES
    x		error-value or integer in [0, 32767], defaults to errno()
    return	string
DESCRIPTION
    If x is the error-value with index n, strerror(x) and strerror(n)
    return one of:
		a system-generated message,
		a calc-generated description,
		a user-defined description created by newerror(str),
		the string "Error n",
    where, in the last form, n is represented decimally.
EXAMPLE
    System error messages may be different for different systems.
    ; errmax(errcount()+3)
	    0
    ; strerror(2)
	"No such file or directory"
    ; x = 3 * ("a" + "b")
    ; print strerror(x)
    Bad arguments for +
    ; a = newerror("alpha")
    ; print strerror(a)
    alpha
    ; print strerror(999)
    Error 999
    ; a = 1/0
    ; print strerror()
    Division by zero
LIMITS
    none
LINK LIBRARY
    none
SEE ALSO
    strcat, strcpy, strlen, strncmp, strncpy, strpos,
    strprintf, strscan, strscanf, substr,
    errcount, errmax, error, iserror, errno, newerror, errorcodes,
    stoponerror
## Copyright (C) 1999-2006  Landon Curt Noll
##
## Calc is open software; you can redistribute it and/or modify it under
## the terms of the version 2.1 of the GNU Lesser General Public License
## as published by the Free Software Foundation.
##
## Calc is distributed in the hope that it will be useful, but WITHOUT
## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
## or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU Lesser General
## Public License for more details.
##
## A copy of version 2.1 of the GNU Lesser General Public License is
## distributed with calc under the filename COPYING-LGPL.  You should have
## received a copy with calc; if not, write to Free Software Foundation, Inc.
## 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
##
## @(#) $Revision: 30.1 $
## @(#) $Id: strerror,v 30.1 2007/03/16 11:10:42 chongo Exp $
## @(#) $Source: /usr/local/src/cmd/calc/help/RCS/strerror,v $
##
## Under source code control:	1996/04/30 03:05:18
## File existed as early as:	1996
##
## chongo <was here> /\oo/\	http://www.isthe.com/chongo/
## Share and enjoy!  :-)	http://www.isthe.com/chongo/tech/comp/calc/
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