Hi again
@C101 Some digging has been done!!
Ok looking at
@uwsearch excellent image catalog we can see something very similar on row eleven.
Title is "White dial 65mm case, 1'' to 30'' dial, one revolution in 30'', 36000BPH"
Items listed as MG1135 (190,191,1290R), MG1183 (191R), MG1555 (1950Rattr)
Looking further into the data from the table on page 2, i think we are close.
First let me say Uwsearch has made a mega effort and has earned many virtual dinners and beers for his collation of data.
Diameter / img/ lap total / BPH/ Left pusher / Right pusher/ both pusher/left bolt/image row ref
From you images #3, 4, 5 and 6
I can partially read a ref LWO ***21?***
Please can you confirm what this read?(LWO 1210 at a guess)
To summaries i believe your have a very nice Nero Lemania
24''' Mouvement
Calibre 1210
a Split-second Chronograph measuring to an 1/10s
Ref 603.
It would be super cool to see the timing sheet.
It would be the first one i've seen and if serial number is on it its a solid data point for dating the watch.
Your dating info is as good as I can do we are reading the same table.
Was this you granddads personal item?
The reason I ask is its missing its case back markings, ie he did not he sign it out from storers.
or have it documented on a clothing certificate as a part of his kit?
All the best
P