It depends where you are in the game.
CANALAVE CITY GYM- CANALAVE LIBRARY [Where Rowan is]
TEAM GALACTIC FIGHT IN LAKE VALOR- THEN GO TO LAKE VERITY [Where Rowan is]
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Go to professor Rowan's place in Sandgem town and talk to him. Then Professor Oak comes and gives you the national pokedex.
beat the elite 4, and you have seen all 210 pokemon, then go and talk to professor rowan in sandgem town. when you do, professor oak will arrive and upgrade your pokedex to the national version. you will also get the ppokeradar.
Go to Sandgem Town and Proffesor Rowan will upgrade your pokedex if you beat the Elite Four.
In Pokemon Platinum on order to get the National Pokedex you have to complete the Sinnoh Pokedex {you don't have to capture them all, you just need to see them and it doesn't matter what gender} then either go to Rowan's PC in a Pokemon Center or visit the Pokemon Research Lab in Sandgem Town and talk to Professor Rowan.
Go to Sandgem Town next to Twinleaf (where you started your adventure) and there should be a building next to the Pokemon Centre there. Go into the lab next to the centre and go forward, you should see an elderly man there, talk to him.
Sandgem town is the second town in Pokemon Diamond/ Pearl/ Platinum. It is the home of Professor Rowan
Professor Rowan's lab is in Sandgem Town, which is north-east of Twinleaf Town. Hope this helps! :D
First see all the Pokemon in The Sinnoh Dex. Then go to Sandgem Town and talk to Professor Rowan. Professor Oak will come and upgrade your Dex to National Dex.
If you fly (or walk ) to Sandgem Town and visit Professor Rowan's Laboratory, Professor Oak will be inside with Prof Rowan and there will be a big conversation and you will receive the National Pokedex. That's all. Please recommend our humble school!
You need to complete the sinnoh pokedex and then talk to professor Rowan in sandgem town
You are supposed to go to Sandgem Town and talk to Professor Rowan, the old thingy.
Once you beat the Pokemon league, go to Sandgem town and go into the lab and talk to Professor Rowan.
You have to Complete the sinnoh pokedex and then see Professor Rowan in his lab at Sandgem town, then another professor from kanto called Professor Oak will give it to you as a gift.
Go to professor Rowan's place in Sandgem town and talk to him. Then Professor Oak comes and gives you the national pokedex.
hi you can find professor rowan in sandgem town,the big house that near the Pokemon center. or if you are went far in the game,later you will see him in canalave city laboratory (the big house that in front of the gym) but he will be there for a very very very short time .oh! don't forget to go and see professor rowan in the sandgem lab once you finish the pokedex because proffessor oak will come and give you the incredible national pokedex!
hes in the building in sandgem town. youll see dawn in front of the building. just go in.
You go to Sandgem town then you go to Professor Rowan's Pokemon Research Lab.You have to talk to him and then Professor Oak will come in and he will give you the National Pokedex (But first you needed to have finish the Sinnoh Pokedex.) P.S When you talk to Professor Rowan he will give you the Pokeradar.