Vintage chronograph movement ID?

[kevkojak]

Here's an unusual one I've recently picked up, a vintage (?) 18ct chronograph.

It's supposedly 1940's but it looks far newer to me. 18ct gold outer case which is so thin that someone has done a gold test on it and pushed a groove in the back!
The inner case is base metal (brass?).

Here's a snap of the movement. Twin register chronograph with the subs at 12 and 6 positions.
Swiss made and the only other marking I can see is under the balance, just a "31" stamp.

Thanks in advance in case anyone can assist.

[stelmo01]

Venus 170 perhaps?


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[kevkojak]

Not a bad shout - it looked a bit crude to be a Venus.

[ibby7]

Just be careful
The minute wheel spring looks bent out of shape. Replacements can be expensive if the cal is rare.

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[kevkojak]

Cheers Ibby. It's going on EBay anyway, not my cup of tea sadly.

[Neil.C]

Yep, Venus movement as has already been stated.

It's a chronographe Swiss style which were base metal with just a thin sheet of 18k (and marked as such) over the top.