Ok, I tried this:

snippet:

...
## easily updated                   ##

our @ISA= qw(Exporter);
our @EXPORT=qw($NPR_TO_DAC $NPR_TO_ADC);

use constant CONST => 2;
...
[download]

but I still got Bareword "CONST" not allowed while "strict subs" in use at ./temp.pl line 10.

So I removed @ISA, and tried use base 'Exporter' instead:

#! /usr/bin/perl

package definitions;

require Exporter;
use base 'Exporter';
use strict;
use warnings;

#################
## definitions ##


our @EXPORT=qw($NPR_TO_DAC $NPR_TO_ADC);

use constant CONST => 2;
use constant CONST2 => 3;
print CONST;
1;
[download]

this gave the same Bareword error.
I think half the problem is that I don't really understand what Exporter is doing or how it works... I have read the documentation, but I'm still somewhat new at this..!
Thankyou for your help so far---any further tips?

I tried your second snippet (copied and pasted to a new script), and it runs!

I have a perl 5.8.8, what's your perl version? And are you sure you tried exactly the same script as you posted here?