Varṇada lagna
There seem to be four ways that varṇada lagna calculation is generally described.
The first method is given in “Studies in Jaimini Astrology”, chapter 2 by B. V. Raman (1986) and “Jaimini Maharishi’s Upadesa Sutras”, verses 4.3.1314 by Sanjay Rath (1997). The calculation there proceeds as follows:

If lagna is in an odd rāśi, let a be the number of rāśis counting forward from Meṣa to lagna; otherwise, let a be the number of rāśis counting backward from Mīna to lagna.

If horā lagna is in an odd rāśi, let b be the number of rāśis counting forward from Meṣa to horā lagna; otherwise, let b be the number of rāśis counting backward from Mīna to horā lagna.

If both lagna and horā lagna are in rāśis of the same parity, let c be the sum of a and b; otherwise, let c be the absolute difference between a and b.

If lagna is in an odd rāśi, count c rāśis forward from Meṣa; otherwise, count c rāśis backward from Mīna.
The second method is given in the translation of Bṛhat Pārāśara Horā Śāstra, verses 6.1316 by Girish Chand Sharma (1999). According to this work, the calculation is as follows (although the example given in the book actually follows the third method described below):

If lagna is in an odd rāśi, let a be the number of rāśis counting forward from Meṣa to lagna; otherwise, let a be the number of rāśis counting backward from Mīna to lagna.

If lagna is in an odd rāśi, let b be the number of rāśis counting forward from Meṣa to horā lagna; otherwise, let b be the number of rāśis counting backward from Mīna to horā lagna.

If both a and b are of the same parity, let c be the sum of a and b; otherwise, let c be the absolute difference between a and b.

If c is odd, count c rāśis forward from Meṣa; otherwise, count c rāśis backward from Mīna.
The third method is given in the translation of Bṛhat Pārāśara Horā Śāstra, verses 5.1013 by R. Santhanam (1984). It is almost the same as the second method, except step 2 is described like so:
 If horā lagna is in an odd rāśi, let b be the number of rāśis counting forward from Meṣa to horā lagna; otherwise, let b be the number of rāśis counting backward from Mīna to horā lagna.
The difference from the second method is that the direction of counting depends on horā lagna instead of lagna. Unfortunately, if we accept this definition of step 2, then the description of step 3 does not seem to be sound, because a and b will always be of the same parity (both will be odd) and, therefore, mentioning the other case is not very useful. Similarly, in step 4 c will always be even and describing the other case is redundant.
The fourth method is given in “Jaimini Sutramritam”, verse 1.1.32 by Iranganti Rangacharya (1995). It is also similar to the second method, except step 4 is identical to that from the first method:
 If lagna is in an odd rāśi, count c rāśis forward from Meṣa; otherwise, count c rāśis backward from Mīna.
There are also other methods, some trying to involve degrees into calculation and that is also mentioned by R. Santhanam and Sanjay Rath in the sources above. A very nice overview of different methods, both described here and others, is available in the article “A Look at the Calculation of Varnada Lagna” by Abhishekha.
Out of all methods described above, Chakra Darshana implements the first method.