Home-brew tool to aid spellcraft, but is it "balanced"?

[MorganS]

I'm wondering if this idea might somehow unbalance things. I can't see how it could, but I thought the Terry Pratchett "Thaum" reference was funny enough to share.

The Thaumatarium

A thaumatarium is a room designed to help wizards conduct magical research and is usually located in a wizards tower.

From the center of the room, a thaumatarium looks like an evenly illuminated room with colorfully patterned walls that hide visual distractions such as doors, windows, and direct light sources.  These colors and patterns are carefully calibrated to improve magical
energy measurements.

A thaum is a measuring unit to quantify magic. It equals the amount of mystical energy required to conjure up one small white pigeon, or three normal-sized billiard balls.  A thaumaturge can use a standard thaumatarium to measure differences in magical energy as small as 10 millithaums.

Using a thaumatarium provides a +2 circumstantial bonus on all types of spellcraft checks.   Creating a thamatarium requires spellcraft 15, Craft(painting) 15. and 500 gp in painting supplies.

Suggestions?

[LazarX]

Yes... make it take about month to do. which is still considerably less than the ceiling of the Sistine Chapel.

[Mr.Alarm]

LazarX wrote:

which is still considerably less than the ceiling of the Sistine Chapel.

Which is massive, incredibly detailed, and made with mundane means. Its basically a non-slot magic item (but I think the fact its not mobile cancels out the non-slot cost) so it should be made using those rules. Your cost is about right, so by the rules it should take a day.

[MorganS]

Now you're talking. I was clearly thinking too small. Maybe this +2 version makes sense but could be a bit more expensive. 1000g would make this a room to be proud of.
But how much for a Sistine Chapel version?

Near epic painting skill would be a must, but how much gold and how long to create!