There are lot of dicussion about Ruf's LOG here

Most people think: it can not replace of IQ test, but will help you for the over the GT denied or HG+ denied
It will give you brief idea about what level gifted kids doing at certain age.

If you read the whole book, it give very detail information about the behaviours of many GT kids

Some other people like to use grade level

like MG: 1-2 grade ahead
HG 3-4,MG 5,PG 6....etc, just rough guid

Probably it is good to re-test, bu private tester use standard test