Device allocation and transformer ratio

Hi All,

I have one long pending query which I am sharing with you.

I have created a from device category which have "type of meas" as semi indirect measurement, it means that a low transformer attached to the device, now my queries are  below.

1 - Should I install a transformer as well  to the installation where the above said device  category's devices are installed.

2- I know the formula and about the transformer ratio but in real scenario how to get the value of transformer ratio ( next to type of meas in device category"

3- In which scenario do we execute the Device allocation TCODE EG72

Thanks

Veer