Figuring out gas oven temperature numbered 1 through 7

The mode selector dial looks more appropriate for an electric oven, but it's still (almost) certainly a "Gas Mark" scale. It used to be common, though modern gas oven usually have Celsius. I know such scales often go hotter, but 7 is high enough for almost all cooking, and I've certainly seen them stop at 7. It's rare for electric ovens to use that scale but not unknown.

The conversion isn't usually quoted precisely, which is throwing you off. The Wikipedia page I've linked above gives the exact conversion but rounding to the nearest 5 or better 10 °C is much more useful.opf a top

Here's a more practical table (rounded to the nearest 10°C), but gas ovens tend to be a little approximate; 1 is about 140°C and 7 about 220°C. If you're still in doubt, you might want to get an oven thermometer, but the suggestions broadly line up with the conversions above (cakes Gas 4-6/180-200°C, roasting 5-7 or 190-220°C, meringue as low as it will go - 140°C is a bit hot really, gas 1/4 is often called for).

In fact given that you want precise temperatures and it's old, maintained for safety (at most) and not performance, an oven thermometer would be a very good idea. This may be a cheap basic model - likely in a rented house and the lack of gas marks 8 and 9 fits with that too. Preheating times can be quite long on some such models.