You can pass numerical attributes to an external command via "Execute new =...".  This external command can then do the math and pass the result _back_ to the logbook either as a new entry or as an edit with the command-line client "elog".

For example, given a new entry with (numerical) attributes A and B, if you have

Execute new = add_them.pl $A $B $message id

in your elog.cfg file, then $A and $B will be passed to the add_them.pl perl script.  Now have the perl script (or bc, or whatever you want to use) do the appropriate math and submit the result.  For example, your perl script might include

$C=$A+$B

$D=$A*$B

elog -a C=$C ... -e "$message id" "Sum as edit"

elog -a D=$D ... "Product as new entry"

Is there any way to directly paste an image from a Windows clipboard into an elog entry page?  It's obvious
for uploading a file, but many of my users say that they never make a file, they just want to paste in an image
already onscreen.

> > Is there any way to directly paste an image from a Windows clipboard into an elog entry page?  It's obvious
> > for uploading a file, but many of my users say that they never make a file, they just want to paste in an image
> > already onscreen.
> 
> This is a limitation of the FCKEditor used inside ELOG, and actually of the whole browser concept under Windows. 
> There are some extensions to Firefox which let your paste an image as an attachment, but none for doing this right 
> into the text body. For some discussion about this have a look at
> 
> http://forums.developer.mindtouch.com/showthread.php?t=188
> 
> for example.

Hmmm.  Well, does that mean that it is easier under Linux?  I have to confess I couldn't figure that out either.  But
I'd be delighted to have Yet Another Reason to tell the users that "it works under Linux, maybe you should switch...."  

Our Unix server died, so we decided to move our old eLog to the new server, running Mac OSX. Elog version is earlier then 2013, I can not say

I read that on OSX  eLog must be intalled through "make" command

if I need to install eLog first, how to add all old information later?