Notification when a field has reached it's limit?

Notification when a field has reached it's limit?

How do notify myself when a field limit is met?

fetch = Registration [Course == input.Course && Finishing == input.Finishing];
num=fetch.Finishing.getall().
size();

{
sendmail
[
from:zoho.adminuserid
to:zoho.adminuserid
subject:"Enter Text Here!!! "
message:"Enter Text Here!!!"
content type:HTML
]
}

How do I send myself an email when the 16 limit is met?

Thanks for any assistance...