I hope this is sufficient. I have the letters in Illustrator so I have to build sentences letter by letter.

I personally think the hybrids work well but I might have to scrap the oldstyle.

Those are the hybrids. The oldstyle numerals are taller.

Seems I made the wrong kind of hybrids then. These are the sets I made:

1 – Caps numerals
2 – Oldstyle numerals (= x-height to cap height)
3 – Hybrids (= slightly taller than x-height)
4 – Small-caps numerals (= x-height)

#1 is indeed lining. #4 is not oldstyle though; those are more like lining numerals for the small-capss/lowercase (the small-caps are x-height size; call them 'petit caps' if you will).

As far as I'm aware it's common for the oldstyle numerals to fit within the x-height with ascending numerals at cap height and descending numerals at lowercase descender height, like I did in #2. They were too unstable for such a mechanical grotesque in my opinion so I designed these quasi-lining lc numerals (#3), hence 'hybrid'.

Should I also design a set of hybrid numerals for the capitals? Initially I wanted to scrap a few sets of numerals but I actually don't mind having such diverse sets.

Man I'm confused.

I think part of the problem might be the way
we're talking about height, as in the overall
height versus what I call the "body" height
(which is like the bottom of the "6").

hhp

A little example from an existing typeface might help:

Thanks for the image. That's all I've been saying though, however my hybrids are smaller, hence I called them small-cap hybrids.

Would people find it useful if I make another set of numerals like the hybrid in the picture? I think then I would have the full range of possibilities of the numerals.

Any words on Celcius?

Get rid of the double story /g/ and the alternate /U/.

/m n h and alikes/ look too dark on top.

Some minor stroke thickness inconsitensies in the light.

Cheers!

There's something "weird" about the "a" of the regular style.
When I look it on the thin style, it works well, the reading "flows".
But when I read the word of above "temperature" there's something that bothers.

See that when you write "I'm a scientist", the "a" still works, because the reader can't see the loop of the eye, which the regular has.

Why don't you try a more simple "a"? like http://www.myfonts.com/fonts/linotype/din-next/pro-regular/glyphs/536654/66

Or maybe, if you want to keep it with that "oval eye", find another way. Right now I believe it's the letter which looks most informal. It needs to be just a little more geometric...
Maybe there's a little too much air above the "eye" of that "a".

That's my opinion, hope it helps!
Best,
Lian.-