In the 737s, we use an "unofficial" thumb rule to check the figures.
The 1st 2 digits of your ATOW [from trim sheet] - 20 gives the V2 +- 3 knots.
For eg, if ATOW = 70,000 Kgs, then V2 would be [70-20] = 150 +- 2 knots. This can be used as a fairly accurate cross-check on whether you entered the figures in the FMC correctly or not. Maybe the 340 also has a thumb rule like this
Cheers