A quick search "RefCombination" will reveal GADS of info.

Here is just a clip of one of Poppabears posts:

RefCombination(int number)

1 = ref X

2 = ref Y

3 = ref X&Y same time,

4 = ref Z

5 = ref X&Z same time

6 = ref Y&Z same time

7 = ref X&Y&Z same time

8 = ref A

9 = ref X&A same time

10 = ref Y&A same time

11 = ref X&Y&A same time

12 = ref Z&A same time

13 = ref X&Z&A same time

14 = ref Y&Z&A same time

15 = ref X&Y&Z&A same time

16 = ref B

17 = ref X&B same time

18 = ref Y&B same time

19 = ref X&Y&B same time

20 = ref Z&B same time

21 = ref X&Z&B same time

22 = ref Y&Z&B same time

23 = ref X&Y&Z&B same time

24 = ref A&B same time

25 = ref X&A&B same time

26 = ref Y&A&B same time

27 = ref X&Y&A&B same time

28 = ref Z&A&B same time

29 = ref X&Z&A&B same time

30 = ref Z&Y&A&B same time

31 = ref X&Y&Z&A&B same time

32 = ref C

33 = ref X&C

34 = ref Y&C

35 = ref X&Y&C,

36 = ref Z&C

37 = ref X&Z&C

38 = ref Y&Z&C

39 = ref X&Y&Z&C

40 = ref A&C

41 = ref X&A&C,

42 = ref Y&A&C

43 = ref X&Y&A&C

44 = ref Z&A&C

45 = ref X&Z&A&C

46 = ref Y&Z&A&C,

47 = ref X&Y&Z&A&C

48 = ref B&C

49 = ref X&B&C

50 = ref Y&B&C

51 = ref X&Y&B&C,

52 = ref Z&B&C

53 = ref X&Z&B&C

54 = ref Y&Z&B&C

55 = ref X&Y&Z&B&C

56 = ref A&B&C,

57 = ref X&A&B&C

58 = ref Y&A&B&C

59 = ref X&Y&A&B&C

60 = ref Z&A&B&C

61 = ref X&Z&A&B&C,

62 = ref Y&Z&A&B&C

63 = ref X&Y&Z&A&B&C