How to tell users that they have to change the focus from the input to apply the change

In HTML, if you have an input with an onchange, it doesn't register the change until you leave (or lose focus) that input. There's an onKeyUp function as well which would have the function run as they type. In my case, this input is affecting a graph that can be quite large at times, and typing in 1000, would have to render the graph for 1, 10, 100, then 1000 very quickly which can slow down the browser quite a bit.

So the problem is when a user types in 1000, nothing changes until they leave the input, press enter or tab. What are some ways that I can tell them this? An 'apply' button seems a bit excessive at times if there are many inputs.