First, a succinct way to do this is to use the between function from Acme::Tools: 
use Acme::Tools;
if (between($frequency, 10, 15) {print "Yes"}

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I believe your code does not print Yes due to operator precedence. My guess is that 
if ($frequency == 10 .. 15) {print "Yes"}

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is the same as: 
if ( ($frequency == 10) .. 15 ) {print "Yes"}

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in which case, the left side of the .. operator ($frequency == 10) is false, and in that case the whole expression is false. Refer to Range Operators.

Update: add another example...

If you set it to 10, you will get a Yes: 

my $frequency = 10;
if ($frequency == 10 .. 15) {print "Yes"}

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but, you will get a warning if you use warnings; In any case, you should not try to use .. this way.

In reply to Re: querying a range of values by toolic
in thread querying a range of values by plendid

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