Thank you for thatIf you use the database of Mikrolisk you find two swiss companies who use this term union soleure. Mikrolisk - The horological trade mark index. Max Studler is registrated in Soloturn and Selzach 1942 as Union SA. Personal this date is a about 5-10 years to late for my personal dating of the watch but who knows, sometimes they are "old fashioned".
Your watch is to me quite typical from outside for a watch of the end 1920 ties - mid thirties. To decide more it would be nice if you open die Backcase to see the movement. Chronometre is writen on the dial but don't espect a outstanding movement. I guess its a good standart flat 15 jewels lever one but we'll see.