Eyepiece Diopter for Nikkormat

Hello All, I’m looking for some help with something. A long time spotmatic user I recently bit the bullet and ordered a Nikkormat, which looks like an awesome beast of a camera. Anyway I have a -1 prescription and prefer to correct the viewfinder with a diopter, but I’m struggling to find my prescription in the round Nikon diopter type. I can find an adjustable option from China but it looks rather flaky. My question: Was the -1.0D option ever available from Nikon and if not what is my best alternative?

I don’t recall a -1 being available because the finder, by design, is -1 diopter. See page 31:

Thanks Brian, I found a Nikon webpage which confirmed that the default is -1 and for my prescription I need a -2 correction lens.

If the standard eyepiece is a -1D strength, then OP would be looking to get -2D in place of -1D if the correction needed for near vision correction is indeed -1D. .
Note that over-the-counter readers are normally PLUS rather than negative value, like +1.0 or +1.5 or +2.75. So if use of +1.0 readers in the drugstore work for OP, the correct Nikon eyepiece should be 0 (and not -2D). The perceived distance in a camera viewfinder ordinarily is about 30" distance or 1m distance (dependent upon manufacturer's design), and the focus screen is NOT at 'infinity'!

Thanks Wilt, I can confirm the correct diopter for my prescription is -2.0D. Found one already on a well known auction site.