Here is link to STR 1D convention card
The idea is that 1C is better as your nebulous bid than 1D. Then putting 1D as your strong bid which is one step higher, the theory is you often get interference and on those hands it doesn't matter whether you opened 1C or 1D.
To get 1C as promising 2+ clubs you would have to open 2D with 5D4M, which I don't think is a good idea. The other option is to open 1M with 4M and 5 or 6D and 2D with a 6+D 1-suiter, which is better but I really like 5-card majors. So I have chosen to make 1C potentially 0C and make it F1 with 1D as a negative or some better hand hands that don't fit into the responding system. 2C is a standard Precision 2C but promises 6+. 2D is an intermediate bid which promises 6+D and denies a 4+ major. Also, 2H/2S are weak 2's. 2N shows both minors 8-12 hcp.
So your strong bid is 1D is artificial 0+D F1, 17+ hcp unbalanced or 18+ hcp balanced
and 1C is:
- 11-14 NV 12-14 Balanced 2+C
12-16 unbalanced 0+C
- 5C possibly with a 4+ card side
- 5+D with a 4+ card side, only 5-card major if a maximum and 6+D
- poor 6+ C/D suit (that isn't good enough for a 2C/2D opening)
- 13-16 minor 2-suiter
- 7-card semi-solid minors with a side A/K
Is artificial, 0+D, F1 and one of -· 0-6 hcp· 11-12 hcp balanced with no 4M and no 5-card suit· 16-18 hcp balanced with no 4M and no 5-card suit