Contact
There is one address and a person reads it.
If a tool is wrong
Please say so, and please include the number you typed and what you believe the right answer is. A specific example is worth far more than a general report, because it can be turned straight into a test that stops the same mistake coming back.
Several of the corrections on this site came in exactly that way. If you tell us a serial that decodes wrongly, the fix and a permanent check against it usually follow together.
If this site uses your work
Several tools rely on research compiled by other people — manufacturers, collectors, and enthusiasts who spent years assembling what nobody else had. Every one of them is named and linked on the page that uses their work.
If that is you and you would rather it were not here, say so and it will be removed. No argument, no negotiation, and you do not need to explain why. That has already happened more than once, and each time the page now points readers to the source instead, which is a worse tool and the right outcome.
If you would like the credit worded differently, that is easier still.
If you are a manufacturer
If this site states something incorrect about your instruments, or reproduces something you would rather it did not, get in touch and it will be dealt with quickly.
If you publish dating information that this site has missed, that is genuinely welcome — going back to the maker has produced a better answer than a third-party compilation every single time it has been possible.
What this address is not for
Valuations and authentication. This site cannot tell you what an instrument is worth or whether it is genuine, and an email will not change that. For anything valuable, a written appraisal from somebody qualified is what you need.