I'd like to have the answer too. I seem to recall that information that the Yamaha jauge at some point (70's) was a gauge differnt from Roslau.(may be due to Suzuki wire ?)
Now in your case if you use US wire you have much more gauges than Roslau, and you need to rescale.
Older types of Pehlmann wire also was different (but yet in 1900xx the gauge was similar.
Most often the differnces are with the thickest numbers , more where used than today.
HEre is a table of correspondence based on gauges and mm dimensions for differnt types of wire, Mapes, Roslau etc.https://docs.google.com/file/d/0B6GjQDkF_AMQVnRFenpzNDdoSkU/edit?usp=sharing
It could be also that the numbers go the other direction, but this is easiluy determined.
The correspondences that are given from Mapes to Roslau gauges are a little approximates, as you can see in the table.
That said you have more gauges with Mapes, a little like with older wire qualities, and that may help to have a good evening of tensions.
I do not have the MOE for Mapes (there are 2 qualities if I understand well) .
Is this considered a secret?. A bass winder told me it is too hard for him to use (it is a part of the "thunder tone of some Steinway in the basses). That should explain the higher iH levels I noticed on a Steinway I have seen recently (it was so high the soprano section was really undefined)
That kind of high ih work well with soft hammers and focus on the attack, the dwell being a less interesting part of the tone then (less clear and pure)
I seem to understand that the European instruments work almost the other way around, the attack is there to provide energy for the dwell, which in the end may be supposed to provide more variability in tone.
A hard attack is driven in a focused sustain, in some case.
Of course playing with an aggressive touch will then give an aggressive tone.
The higher the iH, the sharper the tone, the more we have to voice the attack.
The less the iH, the nicer the tone, but at some point it may get boring and too straight.
The attack is immediately ruled in the rest of the tone.
iH allow some enlargement, as done when tuning unison, and allow the tuner to play with the immediateness of tone projection.
It is also said that iH re conciliate the human ear and justness sensation, with moderate levels in mediums but a definite raise in the treble, that will fight our lesser perception of high frequencies that gives the impression the tone is not strong enough.
Now this iH level progression from mediums to treble and the global level makes instruments more suited for one style or another. dues to the relation with dynamics, also.