How to level a synthesist

[PeteZero]

So I am playing a barbarian1/synthesist1 - when I level to 4th, do I get an ability increase at 4th level and at 6th lvl (5th synthesist) does the eidolon get an ability increase? Just making sure I am doing it right.
Just a sidenote, IIRC a synthesist can take extra evolution, at least I read it somewhere on the boards.

[LazarX]

Stat increases are based on Hit Dice. You level at 4th level and the Eidolon gets a stat bump when it's Hit Dice, not level are in multiples of 4. It's spelled out in the Eidolon advancement chart. Eidolons do not get hit dice every level.

[Kolokotroni]

The synthesist gets the stat increase to HIS OWN STATS. When the eidolon gets to the appropriate HD (see eidolon chart) it will get it's own stat increase. So at level 4 you can increase the summoner's stats not the eidolons. And character with 5 levels of synthesist will be able to add to his eidolons stats (they eidlon gets it's 4th Hit Dice at the summoners 5th level). For you, this would be at least 6th level since you have one level of barbarian.

And yes a synthesist can take extra evolution for his eidolon.