vintage – No1 Pocket Kodak opening 1 to 4, f equivalent stop?

I have a cute little pocket Kodak from the twenties or thirties. It is the bottom of the range model with the "single lens". The opening is not marked in numbers f, but is labeled as 1, 2, 3 and 4.

Is there any way to know the equivalent opening of the number f to measure the exposures with the modern and fast film (Ilford Delta 400)?

I would like to use a 35mm camera as a meter, and decipher a conversion for the vintage camera. The most expensive cameras in the same range have lenses f7.9 and f6.3, so I guess it's higher than that. But I could imagine that a cheap one-element lens was quite bright, but sacrificing sharpness.

No.1 pocket Kodak lens and opening controls

I've done a lot of searching on Google, but I have not found anything. It seems that the other models in the range may have been more common than the "single lens".

I have the original manual, which includes 3 exposure tables for the 3 different lens options (individual, "Kodar f.7.9" and "Kodak Anastigmat f.6.3"), the page for the single lens is reproduced here. However, I realize that the films of the time were quite slow, so this is likely to over-expose the modern movie.

No.1 pocket Kodak single lens exposure guide

Other details of the camera. It takes 120 movies, and it seems to work. I executed an Ilford FP4 roll out of date, and I got 4 or 5 really good images, but I was guessing and exposing exhibitions in full sunlight. I think it says more about the latitude of the movie than my ability with the camera.

The plate that surrounds the lens with the shutter and opening marks has the number "27449".

If you are wondering why the bellows look strange in the photo, it is because they have some light leaks, so I put them in a black paper "vest" that seems to block them enough.

I have a new Ilford Delta 400, and I hope to take portraits with natural light indoors (a very well lit room), the same conditions with a 35mm camera, with a cheap f3.9 lens with Ilford FP4, 125 ASA has not had problems.

Interestingly, the opening is in front of the shutter, which are both in front of the lens element. When holding a ruler and squinting, I assume that the opening in setting 1 is about 8 mm in diameter, and in the setting of 4 about 2 mm.