Reference Tapes - Calibration

One further question. I have a 185nWb calibration tape. Can I use it for the PR99 or should I get a 250nWb?

You can use a 185nWb/m reference tape by calculating the corresponding levels to use - on page6 of this publication, there is a explanation
http://home.comcast.net/~mrltapes/choo&u.pdf