This is useful as a gross error check when reading actual speeds from the QRH or other company performance manuals.

First very simple ones.

For 737-700 V2 is approximately take-off weight - 25.

Same as QRH. Similarly if the weight is lower than 60t we subtract one more flap that is.

Same as QRH. Next printed weight in QRH is 50t which is 2 steps away from ref weight.

Same as QRH. Next weight is 45t.

For this we jump to next flap for the correction.

V2 for 45t: 45-540-535 ie 135 which is only 1 kt less than QRH V2.

Next weight is 40t.

For this we maintain the same correction as if we can not.

Same as QRH. Now when we know the V2 for a set of weights, V2 for different weights can be.

For example: Actual take-off weight.

As we can find out V2 for 50t and 55t and that is 142 and 149.

Starting with 65t the diff between V1 and V2 is 10kts, 60t 11kts, 55t 12kts, 50t 13kts, 45t 15kts, 40t 17kts.

So V1 for 53.5t is 147-13134kts.

The diff between V1 and Vr is just 2 kts up to landing weight of 55t.

Vref 30 - 3 116kts.

Example: Actual weight.

Same as QRHFMC. Vref for flaps 40 for 50t is Vref 30 - 4 130kts.

Diff between Vref 30 and Vref 15 is about 15 kts.) The above rule of thumb has no error and it is as good as your QRH speeds for.

Another example: Act land weight is 49.4t diff is 9.4.

Half of that is 4.7.

Performance Calculator A350