Vetterli--Wetterli
There is also a variant spelling I came across in Italy, back in the 1970s...some older texts name it the "Wetterli" (W instead of V)...The German sound of W is like V in English and Italian...as the Swiss have Four languages, there are also differences of Spelling to accomodate pronunciation; "V" in German is Pronounced "F" ( as in VolksWagen or Vater), but W does not exist in Italian (not officially) and anyway, the name of the Inventor was from the Italian Cantons of Switzerland...hence the "V"...
Just to confuse everyone...
Doc AV
AV Ballistics.