sra: RVS929 (RVS 929); What is this for?

Roger Jones, a guest, has sent me pictures and information about this model RVS929 from SRA, Sweden. It shows a socket for an european 4-pin tube, fitted with a LS7.

It does not really look like an early tube tester. At least the left instrument is playing strongly against ;-) But what is it?

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